Invasion of Poland The Invasion of Poland , also known as the September Campaign or 1939 Defensive War or the Fourth Partition of Poland ( Polish : " Kampania wrześniowa " or " Wojna obronna 1939 roku " or " IV rozbiór Polski " ) in Poland and the Poland Campaign ( German : " Polenfeldzug " ) or Fall Weiss ( Case White ) in Germany , was an invasion of Poland by Germany , the Soviet Union , and a small Slovak contingent that marked the beginning of World War II in Europe . The German invasion began on 1 September 1939 , one week after the signing of the Molotov – Ribbentrop Pact , while the Soviet invasion commenced on 17 September 1939 following the Molotov - Tōgō agreement which terminated the Nomonhan incident on 16 September 1939 . The campaign ended on 6 October 1939 with Germany and the Soviet Union dividing and annexing the whole of Poland . The morning after the Gleiwitz incident , German forces invaded Poland from the north , south , and west . As the Germans advanced , Polish forces withdrew from their forward bases of operation close to the Polish – German border to more established lines of defence to the east . After the mid - September Polish defeat in the Battle of the Bzura , the Germans gained an undisputed advantage . Polish forces then withdrew to the southeast where they prepared for a long defence of the Romanian Bridgehead and awaited expected support and relief from France and the United Kingdom . The two countries had pacts with Poland and had declared war on Germany on 3 September , though in the end their aid to Poland in the September campaign was very limited . The Soviet Red Army ' s invasion of Eastern Poland on 17 September , in accordance with a secret protocol of the Molotov – Ribbentrop Pact , rendered the Polish plan of defence obsolete . Facing a second front , the Polish government concluded the defence of the Romanian Bridgehead was no longer feasible and ordered an emergency evacuation of all troops to neutral Romania . On 6 October , following the Polish defeat at the Battle of Kock , German and Soviet forces gained full control over Poland . The success of the invasion marked the end of the Second Polish Republic , though Poland never formally surrendered . On 8 October , after an initial period of military administration , Germany directly annexed western Poland and the former Free City of Danzig and placed the remaining block of territory under the administration of the newly established General Government . The Soviet Union incorporated its newly acquired areas into its constituent Belarusian and Ukrainian republics , and immediately started a campaign of sovietization . In the aftermath of the invasion , a collective of underground resistance organizations formed the Polish Underground State within the territory of the former Polish state . Many of the military exiles that managed to escape Poland subsequently joined the Polish Armed Forces in the West , an armed force loyal to the Polish government in exile . Prelude to the campaign . In 1933 , the National - Socialist German Workers ' Party , under its leader Adolf Hitler , came to power in Germany . As early as the autumn of 1933 Hitler envisioned annexing such territories as Bohemia , Western Poland , Austria to Germany and creation of satellite or puppet state s without economies or policies of their own . As part of this long term policy , Hitler at first pursued a policy of rapprochement with Poland , trying to improve German – Polish relations , culminating in the German – Polish Non - Aggression Pact of 1934 . Earlier , Hitler ' s foreign policy worked to weaken ties between Poland and France , and attempted to manoeuvre Poland into the Anti - Comintern Pact , forming a cooperative front against the Soviet Union . Poland would be granted territory of its own , to its northeast in Ukraine and Belarus if it agreed to wage war against Soviet Union , but the concessions the Poles were expected to make meant that their homeland would become largely dependent on Germany , functioning as little more than a client state . The Poles feared that their independence would eventually be threatened altogether . To provoke war with Poland in order to gain Lebensraum , Nazis used as a pretext a claim to Free City of Danzig and Polish territory that separated German exclave of East Prussia from the rest of the Reich . The so - called Polish Corridor constituted land long disputed by Poland and Germany , and inhabited by a Polish majority . The Corridor became a part of Poland after the Treaty of Versailles . Many Germans also wanted the city of Danzig and its environs ( together the Free City of Danzig ) to be reincorporated into Germany . Danzig was a port city with a German majority . It had been separated from Germany after Versailles and made into a nominally independent Free City of Danzig . Hitler sought to use this as reason for war , reverse these territorial losses , and on many occasions made an appeal to German nationalism , promising to " liberate " the German minority still in the Corridor , as well as Danzig . Poland participated in the partition of Czechoslovakia that followed the Munich Agreement , although they were not part of the agreement . It coerced Czechoslovakia to surrender the region of Český Těšín by issuing an ultimatum to that effect on 30 September 1938 , which was accepted by Czechoslovakia on 1 October . By 1937 , Germany began to increase its demands for Danzig , while proposing that a roadway be built in order to connect East Prussia with Germany proper , running through the Polish Corridor . Poland rejected this proposal , fearing that after accepting these demands , it would become increasingly subject to the will of Germany and eventually lose its independence as the Czechs had . Polish leaders also distrusted Hitler . Furthermore , Germany ' s collaboration with anti - Polish Ukrainian nationalists from the Organization of Ukrainian Nationalists , which was seen as an effort to isolate and weaken Poland , weakened Hitler ' s credibility from the Polish point of view . The British were also aware of the situation between Germany and Poland . On 31 March 1939 the Anglo - Polish military alliance was formed by Britain and France , ensuring that Polish independence and territorial integrity would be defended with their support if it were to be threatened by Germany . On the other hand , British Prime Minister Neville Chamberlain and his Foreign Secretary , Lord Halifax , still hoped to strike a deal with Hitler regarding Danzig ( and possibly the Polish Corridor ) , and Hitler hoped for the same . Chamberlain and his supporters believed war could be avoided and hoped Germany would agree to leave the rest of Poland alone . German hegemony over Central Europe was also at stake . In private Hitler revealed in May that Danzig was not the real issue to him , but pursuit of Lebensraum for Germany With tensions mounting , Germany turned to aggressive diplomacy as well . On 28 April 1939 , it unilaterally withdrew from both the German - Polish Non - Aggression Pact of 1934 and the London Naval Agreement of 1935 . Talks over Danzig and the Corridor broke down and months passed without diplomatic interaction between Germany and Poland . During this interim , the Germans learned that France and Britain had failed to secure an alliance with the Soviet Union against Germany , and that the Soviet Union was interested in an alliance with Germany against Poland . Hitler had already issued orders to prepare for a possible " solution of the Polish problem by military means " — a Case White scenario . In May 1939 , in a statement to his generals while they were in the midst of planning the invasion of Poland , Hitler made it clear that the invasion would not come without resistance as it had in Czechoslovakia : With minor exceptions German national unification has been achieved . Further successes cannot be achieved without bloodshed . Poland will always be on the side of our adversaries . . . Danzig is not the objective . It is a matter of expanding our living space in the east , of making our food supply secure , and solving the problem of the Baltic states . To provide sufficient food you must have sparsely settled areas . There is therefore no question of sparing Poland , and the decision remains to attack Poland at the first opportunity . We cannot expect a repetition of Czechoslovakia . There will be fighting . However , with the surprise signing of the Molotov - Ribbentrop Pact on 23 August , the denouncement of secret Nazi - Soviet talks held in Moscow , Germany neutralized the possibility of Soviet opposition to a campaign against Poland and war became imminent . In fact , the Soviets agreed to aid Germany in the event of France or the UK going to war with Germany over Poland and , in a secret protocol of the pact , the Germans and the Soviets agreed to divide Eastern Europe , including Poland , into two spheres of influence ; the western ⅓ of the country was to go to Germany and the eastern ⅔ to the Soviet Union . The German assault was originally scheduled to begin at 04 : 00 on 26 August . However , on 25 August , the Polish - British Common Defense Pact was signed as an annex to the Franco - Polish Military Alliance . In this accord , Britain committed itself to the defence of Poland , guaranteeing to preserve Polish independence . At the same time , the British and the Poles were hinting to Berlin that they were willing to resume discussions — not at all how Hitler hoped to frame the conflict . Thus , he wavered and postponed his attack until 1 September , managing to in effect halt the entire invasion " in mid - leap " . However , there was one exception : in the night of 25 – 6 August , a German sabotage group which had not heard anything about a delay of the invasion made an attack on the Jablunkov Pass and Mosty railway station in Silesia . On the morning of 26 August , this group was repelled by Polish troops . The German side described all this as an incident " caused by an insane individual " ( see Jabłonków Incident ) . On 26 August , Hitler tried to dissuade the British and the French from interfering in the upcoming conflict , even pledging that the " Wehrmacht " forces would be made available to Britain ' s empire in the future . The negotiations convinced Hitler that there was little chance the Western Allies would declare war on Germany , and even if they did , because of the lack of " territorial guarantees " to Poland , they would be willing to negotiate a compromise favourable to Germany after its conquest of Poland . Meanwhile , the increased number of overflights by high - altitude reconnaissance aircraft and cross border troop movements signaled that war was imminent . On 29 August , prompted by the British , Germany issued one last diplomatic offer , with " Fall Weiss " " Case White " yet to be rescheduled . That evening , the German government responded in a communication that it aimed not only for the restoration of Danzig but also the Polish Corridor ( which had not previously been part of Hitler ’ s demands ) in addition to the safeguarding of the German minority in Poland . It said that they were willing to commence negotiations , but indicated that a Polish representative with the power to sign an agreement had to arrive in Berlin the next day while in the meantime it would draw up a set of proposals . The British Cabinet was pleased that negotiations had been agreed to but , mindful of how Emil Hacha had been forced to sign his country away under similar circumstances just months earlier , regarded the requirement for an immediate arrival of a Polish representative with full signing powers as an unacceptable ultimatum . On the night of 30 / 31 August , German Foreign Minister Joachim von Ribbentrop read a 16 - point German proposal to the British ambassador . When the ambassador requested a copy of the proposals for transmission to the Polish government Ribbentrop refused on the grounds that the requested Polish representative had failed to arrive by midnight . When Polish Ambassador Lipski went to see Ribbentrop later on 31 August to indicate that Poland was favorably disposed to negotiations , he announced that he did not have the full power to sign , and Ribbentrop dismissed him . It was then broadcast that Poland had rejected Germany ' s offer , and negotiations with Poland came to an end . Hitler issued orders for the invasion to commence soon afterwards . On 29 August , German saboteurs planted a bomb at the railway station in Tarnów and killed 21 passengers , leaving 35 wounded . On 30 August , the Polish Navy sent its destroyer flotilla to Britain , executing Operation Peking . On the same day , Marshal of Poland Edward Rydz - Śmigły announced the mobilization of Polish troops . However , he was pressured into revoking the order by the French , who apparently still hoped for a diplomatic settlement , failing to realize that the Germans were fully mobilized and concentrated at the Polish border . During the night of 31 August , the Gleiwitz incident , a false flag attack on the radio station , was staged near the border city of Gleiwitz by German units posing as Polish troops , in Upper Silesia as part of the wider Operation Himmler . On 31 August 1939 , Hitler ordered hostilities against Poland to start at 4 : 45 the next morning . Because of the prior stoppage , Poland managed to mobilize only 70 % of its planned forces , and many units were still forming or moving to their designated frontline positions . Opposing forces . Germany . Germany had a substantial numeric advantage over Poland and had developed a significant military prior to the conflict . The " Heer " ( army ) had some 2 , 400 tank s organized into six " panzer " divisions , utilizing a new operational doctrine . It held that these divisions should act in coordination with other elements of the military , punching holes in the enemy line and isolating selected units , which would be encircled and destroyed . This would be followed up by less - mobile mechanized infantry and foot soldiers . The " Luftwaffe " ( air force ) provided both tactical and strategic air power , particularly dive bomber s that disrupted lines of supply and communications . Together , the new methods were nicknamed " " Blitzkrieg " " ( lightning war ) . Historian Basil Liddell Hart claimed " Poland was a full demonstration of the " Blitzkrieg " theory . " Some other historians , however , disagree . Aircraft played a major role in the campaign . Bombers also attacked cities , causing huge losses amongst the civilian population . The " Luftwaffe " forces consisted of 1 , 180 fighter s , 290 Ju 87 " Stuka " dive bomber s , 1 , 100 conventional bombers ( mainly Heinkel He 111 s and Dornier Do 17 s ) , and an assortment of 550 transport and 350 reconnaissance aircraft . In total , Germany had close to 4 , 000 aircraft , most of them modern . A force of 2 , 315 aircraft was assigned to " Weiss " . Due to its prior participation in the Spanish Civil War , the " Luftwaffe " was probably the most experienced , best trained and best equipped air force in the world in 1939 . Poland . Between 1936 and 1939 , Poland invested heavily in the Central Industrial Region . Preparations for a defensive war with Germany were ongoing for many years , but most plans assumed fighting would not begin before 1942 . To raise funds for industrial development , Poland sold much of the modern equipment it produced . In 1936 , a National Defence Fund was set up to collect funds necessary for strengthening the Polish Armed forces . The Polish Army had approximately a million soldiers , but less than half were mobilized by 1 September . Latecomers sustained significant casualties when public transport became targets of the " Luftwaffe " . The Polish military had fewer armored forces than the Germans , and these units , dispersed within the infantry , were unable to effectively engage the enemy . Experiences in the Polish - Soviet War shaped Polish Army organizational and operational doctrine . Unlike the trench warfare of World War I , the Polish - Soviet War was a conflict in which the cavalry ' s mobility played a decisive role . Poland acknowledged the benefits of mobility but was unable to invest heavily in many of the expensive , unproven inventions since then . In spite of this , Polish cavalry brigade s were used as a mobile mounted infantry and had some successes against both German infantry and cavalry . The Polish Air Force ( " Lotnictwo Wojskowe " ) was at a severe disadvantage against the German " Luftwaffe " , although it was not destroyed on the ground early on , as is commonly believed . The Polish Air Force lacked modern fighters , but its pilots were among the world ' s best trained , as proven a year later in the Battle of Britain , in which the Poles played a major part . Overall , the Germans enjoyed numerical and qualitative aircraft superiority . Poland had only about 600 aircraft , of which only 37 P - 37 " Łoś " bombers were modern and comparable to its German counterparts . The Polish Air Force had roughly 185 PZL P . 11 and some 95 PZL P . 7 fighters , 175 PZL . 23 " Karaś " Bs , 35 " Karaś " As , and by September , over 100 PZL . 37s were produced . However , for the September Campaign , only some 70 % of those aircraft were mobilized . Only 36 PZL . 37s were deployed . All those aircraft were of indigenous Polish design , with the bombers being more modern than fighters , according to the Ludomił Rayski air force expansion plan , which relied on a strong bomber force . The Polish fighters were a generation older than their German counterparts ; the PZL P . 11 fighter — produced in the early 1930s — had a top speed of only , far less than German bombers . To compensate , the pilots relied on its maneuverability and high diving speed . The tank force consisted of two armored brigades , four independent tank battalions and some 30 companies of TKS tankettes attached to infantry divisions and cavalry brigades . The Polish Navy was a small fleet of destroyer s , submarine s and smaller support vessels . Most Polish surface units followed Operation Peking , leaving Polish ports on 20 August and escaping by way of the North Sea to join with the British Royal Navy . Submarine forces participated in Operation Worek , with the goal of engaging and damaging German shipping in the Baltic Sea , but they had much less success . In addition , many merchant marine ships joined the British merchant fleet and took part in wartime convoys . Details of the campaign . German plan . The September Campaign was devised by General Franz Halder , chief of the general staff , and directed by General Walther von Brauchitsch , the commander in chief of the upcoming campaign . It called for the start of hostilities before a declaration of war , and pursued a doctrine of mass encirclement and destruction of enemy forces . The infantry — far from completely mechanized but fitted with fast moving artillery and logistic support — was to be supported by " Panzers " and small numbers of truck - mounted infantry ( the " Schützen " regiments , forerunners of the " panzergrenadier s " ) to assist the rapid movement of troops and concentrate on localized parts of the enemy front , eventually isolating segments of the enemy , surrounding , and destroying them . The pre - war " armored idea " ( which an American journalist in 1939 dubbed " Blitzkrieg " ) — which was advocated by some generals , including Heinz Guderian — would have had the armor punching holes in the enemy ' s front and ranging deep into rear areas ; in actuality , the campaign in Poland would be fought along more traditional lines . This stemmed from conservatism on the part of the German high command , who mainly restricted the role of armor and mechanized forces to supporting the conventional infantry divisions . Poland ' s terrain was well suited for mobile operations when the weather cooperated ; the country had flat plain s with long frontiers totalling almost , Poland ' s long border with Germany on the west and north — facing East Prussia — extended . Those had been lengthened by another on the southern side in the aftermath of the Munich Agreement of 1938 . The German incorporation of Bohemia and Moravia and creation of the German puppet state of Slovakia meant that Poland ' s southern flank was exposed . Hitler demanded that Poland be conquered in six weeks , but German planners thought that it would require three months . They intended to fully exploit their long border with the great enveloping manoeuver of " Fall Weiss " . German units were to invade Poland from three directions : All three assaults were to converge on Warsaw , while the main Polish army was to be encircled and destroyed west of the Vistula . " Fall Weiss " was initiated on 1 September 1939 , and was the first operation of World War II in Europe . Polish defence plan . The Polish political determination to deploy forces directly at the German - Polish border , based on the Polish - British Common Defense Pact , shaped the country ' s defence plan , " Plan West " . Poland ' s most valuable natural resources , industry and population were located along the western border in Eastern Upper Silesia . Polish policy centred on their protection especially since many politicians feared that if Poland were to retreat from the regions disputed by Germany , Britain and France would sign a separate peace treaty with Germany similar to the Munich Agreement of 1938 . The fact that none of Poland ' s allies had specifically guaranteed Polish borders or territorial integrity certainly did not help in easing Polish concerns . For these reasons , Poland disregarded French advice to deploy the bulk of their forces behind the natural barriers such as the Vistula and San rivers , even though some Polish generals supported it as a better strategy . The West Plan did permit the Polish armies to retreat inside the country , but it was supposed to be a slow retreat behind prepared positions and was intended to give the armed forces time to complete its mobilization and execute a general counteroffensive with the support of the Western Allies . The Polish General Staff had not begun elaborating the " West " defence plan until 4 March 1939 . It was assumed that the Polish Army , fighting in the initial phase of the war alone , would be compelled to defend the western regions of the country . The plan of operations took into account , first of all , the numerical and material superiority of the enemy and , consequently , assumed the defensive character of Polish operations . The Polish intentions were : the defence of the western regions judged as indispensable for waging the war , the taking advantage of the propitious conditions for counterblows by reserve units , the avoidance of being smashed before the beginning of Allied operations in the West and the making of decisions depending of the existing situation . The operational plan had not been elaborated in detail and concerned only the first stage of operations . The British and French estimated that Poland should be able to defend itself for two to three months , while Poland estimated it could do so for at least six months . Poland drafted its estimates based upon the expectation that the Western Allies honor their treaty obligations and quickly start an offensive of their own . In addition , the French and British expected the war to develop into trench warfare much like World War I . The Polish government was not notified of this strategy and based all of its defence plans on promises of quick relief by their Western allies . Polish forces were stretched thinly along the Polish - German border and lacked compact defence lines and good defence positions along disadvantageous terrain . This strategy also left supply line s poorly protected . One - third of Poland ' s forces were massed in or near the Polish Corridor , making them vulnerable to a double envelopment from East Prussia and the west . Another third were concentrated in the north - central part of the country , between the major cities of Łódź and Warsaw . The forward positioning of Polish forces vastly increased the difficulty of carrying out strategic maneuvers , compounded by inadequate mobility , as Polish units often lacked the ability to retreat from their defensive positions as they were being overrun by more mobile German mechanized formations . As the prospect of conflict increased , the British government pressed Marshal Edward Rydz - Śmigły to evacuate the most modern elements of the Polish Navy from the Baltic Sea . In the event of war the Polish military leaders realized that the ships which remained in the Baltic were likely to be quickly sunk by the Germans . Furthermore , the Danish straits were well within operating range of the German " Kriegsmarine " and " Luftwaffe " , so there was little chance of an evacuation plan succeeding if implemented after hostilities began . Four days after the signing of the Polish - British Common Defense Pact , three destroyers of the Polish Navy executed the Peking Plan and consequently evacuated to Great Britain . Although the Polish military had prepared for conflict , the civilian population remained largely unprepared . Polish pre - war propaganda emphasized that any German invasion would be easily repelled . Consequently , Polish defeats during the German invasion came as a shock to the civilian population . Lacking training for such a disaster , the civilian population panicked and retreated east , spreading chaos , lowering troop morale and making road transportation for Polish troops very difficult . Phase 1 : German invasion . Following several German - staged incidents ( like the Gleiwitz incident , a part of Operation Himmler ) , which German propaganda used as an excuse to claim that German forces were acting in self - defence , the first regular act of war took place on 1 September 1939 , at 04 : 40 , when the " Luftwaffe " attacked the Polish town of Wieluń , destroying 75 % of the city and killing close to 1 , 200 people , most of them civilians . This invasion subsequently began World War II . Five minutes later , the old German pre - dreadnought battleship " Schleswig - Holstein " opened fire on the Polish military transit depot at Westerplatte in the Free City of Danzig on the Baltic Sea . At 08 : 00 , German troops — still without a formal declaration of war issued — attacked near the Polish town of Mokra . The Battle of the Border had begun . Later that day , the Germans attacked on Poland ' s western , southern and northern borders , while German aircraft began raids on Polish cities . The main axis of attack led eastwards from Germany proper through the western Polish border . Supporting attacks came from East Prussia in the north , and a co - operative German - Slovak tertiary attack by units ( Field Army " Bernolák " ) from German - allied Slovakia in the south . All three assaults converged on the Polish capital of Warsaw . The Allied governments declared war on Germany on 3 September ; however , they failed to provide any meaningful support . The German - French border saw only a few minor skirmishes , although the majority of German forces , including 85 % of their armoured forces , were engaged in Poland . Despite some Polish successes in minor border battles , German technical , operational and numerical superiority forced the Polish armies to retreat from the borders towards Warsaw and Lwów . The " Luftwaffe " gained air superiority early in the campaign . By destroying communications , the " Luftwaffe " increased the pace of the advance which overran Polish airstrips and early warning sites , causing logistical problems for the Poles . Many Polish Air Force units ran low on supplies , 98 of their number withdrew into then - neutral Romania . The Polish initial strength of 400 was reduced to just 54 by 14 September and air opposition virtually ceased . By 3 September , when Günther von Kluge in the north had reached the Vistula river ( some from the German border at that time ) and Georg von Küchler was approaching the Narew River , Walther von Reichenau ' s armor was already beyond the Warta river ; two days later , his left wing was well to the rear of Łódź and his right wing at the town of Kielce . By 8 September , one of his armored corps — having advanced in the first week of the campaign — reached the outskirts of Warsaw . Light divisions on Reichenau ' s right were on the Vistula between Warsaw and the town of Sandomierz by 9 September while List — in the south — was on the San River above and below the town of Przemyśl . At the same time , Guderian led his 3rd Army tanks across the Narew , attacking the line of the Bug River , already encircling Warsaw . All the German armies made progress in fulfilling their parts of the " Fall Weiss " plan . The Polish armies were splitting up into uncoordinated fragments , some of which were retreating while others were launching disjointed attacks on the nearest German columns . Polish forces abandoned the regions of Pomerelia ( the Polish Corridor ) , Greater Poland and Polish Upper Silesia in the first week . The Polish plan for border defence was proven a dismal failure . The German advance as a whole was not slowed . On 10 September , the Polish commander - in - chief — Marshal Edward Rydz - Śmigły — ordered a general retreat to the southeast , towards the so - called Romanian Bridgehead . Meanwhile , the Germans were tightening their encirclement of the Polish forces west of the Vistula ( in the Łódź area and , still farther west , around Poznań ) and also penetrating deeply into eastern Poland . Warsaw — under heavy aerial bombardment since the first hours of the war — was attacked on 9 September and was put under siege on 13 September . Around that time , advanced German forces also reached the city of Lwów , a major metropolis in eastern Poland . 1 , 150 German aircraft bombed Warsaw on 24 September . The Polish defensive plan called for a strategy of encirclement : they were to allow the Germans to advance in between two Polish Army groups in the line between Berlin and Warsaw - Lodz , at which point Armia Prusy would move in and repulse the German spearhead , trapping them . In order for this to happen , Armia Prusy needed to be fully mobilized by 3 September . However , Polish military planners failed to foresee the speed of the German advance and predicted that Armia Prusy would need to be fully mobilized by 16 September , by which time it was too late . The largest battle during this campaign — the Battle of Bzura — took place near the Bzura river west of Warsaw and lasted 9 – 19 September . Polish armies " Poznań " and " Pomorze " , retreating from the border area of the Polish Corridor , attacked the flank of the advancing German 8th Army , but the counterattack failed after initial success . After the defeat , Poland lost its ability to take the initiative and counterattack on a large scale . German air power was instrumental during the battle . The " Luftwaffe " s offensive broke what remained of Polish resistance in an " awesome demonstration of air power " . The " Luftwaffe " quickly destroyed the bridges across the Bzura River . Afterward , the Polish forces were trapped out in the open , and were attacked by wave after wave of " Stukas " , dropping " light bombs " which caused huge numbers of casualties . The Polish anti - aircraft batteries ran out of ammunition and retreated to the forests , but were then " smoked out " by the Heinkel He 111 and Dornier Do 17 s dropping incendiaries . The " Luftwaffe " left the army with the task of mopping up survivors . The " Stukageschwaders " alone dropped of bombs during this battle . The Polish government ( of President Ignacy Mościcki ) and the high command ( of Marshal Edward Rydz - Śmigły ) left Warsaw in the first days of the campaign and headed southeast , reaching Lublin on 6 September . From there , it moved on 9 September to Kremenez , and on 13 September to Zaleshiki on the Romanian border . Rydz - Śmigły ordered the Polish forces to retreat in the same direction , behind the Vistula and San rivers , beginning the preparations for the long defense of the Romanian Bridgehead area . Phase 2 : after Soviet Union invaded from the east . From the beginning , the German government repeatedly asked Vyacheslav Molotov whether the Soviet Union would keep to its side of the partition bargain . The Soviet forces were holding fast along their designated invasion points pending finalization of the five - month - long undeclared war with Japan in the far east . On 15 September 1939 the Ambassadors Molotov and Shigenori Tōgō completed their agreement ending the conflict , and the Nomonhan cease - fire went into effect on 16 September 1939 . Now cleared of any " second front " threat from the Japanese , Soviet premier Joseph Stalin ordered his forces into Poland on 17 September . It was agreed that the USSR would relinquish its interest in the territories between the new border and Warsaw in exchange for inclusion of Lithuania in the Soviet " zone of interest " . By 17 September , the Polish defence was already broken and the only hope was to retreat and reorganize along the Romanian Bridgehead . However , these plans were rendered obsolete nearly overnight , when the over 800 , 000 strong Soviet Red Army entered and created the Belarussian and Ukrainian fronts after invading the eastern regions of Poland in violation of the Riga Peace Treaty , the Soviet - Polish Non - Aggression Pact , and other international treaties , both bilateral and multilateral . Soviet diplomacy claimed that they were " protecting the Ukrainian and Belarusian minorities of eastern Poland since the Polish government had abandoned the country and the Polish state ceased to exist " . Polish border defence forces in the east — known as the " Korpus Ochrony Pogranicza " — consisted of about 25 battalions . Edward Rydz - Śmigły ordered them to fall back and not engage the Soviets . This , however , did not prevent some clashes and small battles , such as the Battle of Grodno , as soldiers and local population attempted to defend the city . The Soviets murdered numerous Polish officers , including prisoners of war like General Józef Olszyna - Wilczyński . The Organization of Ukrainian Nationalists rose against the Poles , and communist partisans organized local revolts , robbing and murdering Poles . Those movements were quickly disciplined by the NKVD . The Soviet invasion was one of the decisive factors that convinced the Polish government that the war in Poland was lost . Prior to the Soviet attack from the east , the Polish military ' s fall - back plan had called for long - term defence against Germany in the south - eastern part of Poland , while awaiting relief from a Western Allies attack on Germany ' s western border . However , the Polish government refused to surrender or negotiate a peace with Germany . Instead , it ordered all units to evacuate Poland and reorganize in France . Meanwhile , Polish forces tried to move towards the Romanian Bridgehead area , still actively resisting the German invasion . From 17 – 20 September , Polish armies " Kraków " and " Lublin " were crippled at the Battle of Tomaszów Lubelski , the second largest battle of the campaign . The city of Lwów capitulated on 22 September because of Soviet intervention ; the city had been attacked by the Germans over a week earlier , and in the middle of the siege , the German troops handed operations over to their Soviet allies . Despite a series of intensifying German attacks , Warsaw — defended by quickly reorganized retreating units , civilian volunteers and militia — held out until 28 September . The Modlin Fortress north of Warsaw capitulated on 29 September after an intense 16 - day battle . Some isolated Polish garrison s managed to hold their positions long after being surrounded by German forces . Westerplatte enclave ' s tiny garrison capitulated on 7 September and the Oksywie garrison held until 19 September ; Hel Fortified Area was defended until 2 October . In the last week of September , Hitler made a speech in the city of Danzig in which he said : Poland never will rise again in the form of the Versailles treaty . That is guaranteed not only by Germany , but also … Russia . Despite a Polish victory at the Battle of Szack , after which the Soviets executed all the officers and NCOs they had captured , the Red Army reached the line of rivers Narew , Bug River , Vistula and San by 28 September , in many cases meeting German units advancing from the other direction . Polish defenders on the Hel peninsula on the shore of the Baltic Sea held out until 2 October . The last operational unit of the Polish Army , General Franciszek Kleeberg ' s " Samodzielna Grupa Operacyjna " Polesie " " , surrendered after the four - day Battle of Kock near Lublin on 6 October marking the end of the September Campaign . Civilian losses . The Polish September Campaign was an instance of total war . Consequently , civilian casualties were high during and after combat . From the start , the " Luftwaffe " attacked civilian targets and columns of refugees along the roads to wreak havoc , disrupt communications , and target Polish morale . Apart from the victims of battles , the German forces ( both SS and the regular " Wehrmacht " ) murdered several thousand Polish civilians . During Operation Tannenberg , nearly 20 , 000 Poles were shot at 760 mass execution sites by the " Einsatzgruppen " . The Polish Campaign was the first action by Adolf Hitler in his attempt to create Lebensraum , or living space , for the ethnic German people . The German retaliation against the opposing Polish civilians quickly turned into an atrocity , an irregular warfare against Polish men , women , and children . The brutality that the German army carried out on the civilians was justifiable in their eyes . Many historians have studied the reasoning behind this brutality and have found that Nazi propaganda could be one of the factors . Nazi propaganda worked to manipulate the German people into believing that the Jewish and other ethnic people were the enemy Altogether , the civilian losses of Polish population amounted to about 150 , 000 – 200 , 000 while German civilian losses amounted to roughly 3 , 250 ( including 2 , 000 who died fighting Polish troops as members of a fifth column ) . Aftermath . Poland was divided among Germany , the Soviet Union , and Slovakia . Lithuania received the city of Wilno and its environs on 28 October 1939 from the Soviet Union . On 8 and 13 September 1939 , the German military districts of " " Posen " " ( Poznan ) — commanded by General Alfred von Vollard - Bockelberg — and " " Westpreußen " " ( West Prussia ) — commanded by General Walter Heitz — were established in conquered Greater Poland and Pomerelia , respectively . Based on laws of 21 May 1935 and 1 June 1938 , the German " Wehrmacht " shared its administrative powers with civilian " chief civil administrators " ( " Chefs der Zivilverwaltung , CdZ " ) . German dictator Adolf Hitler appointed Arthur Greiser to become the CdZ of the Posen military district , and Danzig ' s " Gauleiter " Albert Forster to become the CdZ of the West Prussian military district . On 3 October , the military districts " Lodz " and " Krakau " ( Cracow ) were set up under command of " Generalobersten " ( Colonel - Generals ) ) Gerd von Rundstedt and Wilhelm List , and Hitler appointed Hans Frank and Arthur Seyss - Inquart as civil heads , respectively . At the same time , Frank was appointed " supreme chief administrator " for all occupied territories . On 28 September , another secret German - Soviet protocol modified the arrangements of August : all of Lithuania was shifted to the Soviet sphere of influence ; in exchange , the dividing line in Poland was moved in Germany ' s favour , eastwards towards the Bug River . On 8 October , Germany formally annexed the western parts of Poland with Greiser and Forster as " Reichsstatthalter " , while the south - central parts were administered as the General Government led by Frank . Even though water barriers separated most of the spheres of interest , the Soviet and German troops met on numerous occasions . The most remarkable event of this kind occurred at Brest - Litovsk on 22 September . The German 19th " Panzer " Corps — commanded by General Heinz Guderian — had occupied the city , which lay within the Soviet sphere of interest . When the Soviet 29th Tank Brigade — commander by S . M . Krivoshein — approached , the commanders negotiated that the German troops would withdraw and the Soviet troops would enter the city saluting each other . At Brest - Litovsk , Soviet and German commanders held a joint victory parade before German forces withdrew westward behind a new demarcation line . Just three days earlier , however , the parties had a more hostile encounter near Lwow ( " Lviv , Lemberg " ) , when the German 137th " Gebirgsjägerregimenter " ( mountain infantry regiment ) attacked a reconnaissance detachment of the Soviet 24th Tank Brigade ; after a few casualties on both sides , the parties turned to negotiations . The German troops left the area , and the Red Army troops entered Lviv on 22 September . The Molotov – Ribbentrop pact and the invasion of Poland marked the beginning of a period during which the government of the Soviet Union increasingly tried to convince itself that the actions of Germany were reasonable , and were not developments to be worried about , despite evidence to the contrary . On 7 September 1939 , just a few days after France and Britain joined the war against Germany , Stalin explained to a colleague that the war was to the advantage of the Soviet Union , as follows : About 65 , 000 Polish troops were killed in the fighting , with 420 , 000 others being captured by the Germans and 240 , 000 more by the Soviets ( for a total of 660 , 000 prisoners ) . Up to 120 , 000 Polish troops escaped to neutral Romania ( through the Romanian Bridgehead and Hungary ) , and another 20 , 000 to Latvia and Lithuania , with the majority eventually making their way to France or Britain . Most of the Polish Navy succeeded in evacuating to Britain as well . German personnel losses were less than their enemies ( ~ 16 , 000 KIA ) . None of the parties to the conflict — Germany , the Western Allies or the Soviet Union — expected that the German invasion of Poland would lead to a war that would surpass World War I in its scale and cost . It would be months before Hitler would see the futility of his peace negotiation attempts with the United Kingdom and France , but the culmination of combined European and Pacific conflicts would result in what was truly a " world war " . Thus , what was not seen by most politicians and generals in 1939 is clear from the historical perspective : The Polish September Campaign marked the beginning of the Second World War in Europe , which combined with the Japanese invasion of China in 1937 and the Pacific War in 1941 , formed the cataclysm known as World War II . The invasion of Poland led Britain and France to declare war on Germany on 3 September . However , they did little to affect the outcome of the September Campaign . No declaration of war was issued by Britain and France against the Soviet Union . This lack of direct help led many Poles to believe that they had been betrayed by their Western allies . On 23 May 1939 , Hitler explained to his officers that the object of the aggression was not Danzig , but the need to obtain German " Lebensraum " and details of this concept would be later formulated in the infamous " Generalplan Ost " . The invasion decimated urban residential areas , civilians soon became indistinguishable from combatants , and the forthcoming German occupation ( both on the annexed territories and in the General Government ) was one of the most brutal episodes of World War II , resulting in between 5 . 47 million and 5 . 67 million Polish deaths ( about 20 % of the country ' s " total " population , and over 90 % of its Jewish minority ) — including the mass murder of 3 million Polish citizens ( mainly Jews as part of the final solution ) in extermination camp s like Auschwitz , in concentration camps , and in numerous ad hoc massacres , where civilians were rounded up , taken to a nearby forest , machine - gunned , and then buried , whether they were dead or not . According to the Polish Institute of National Remembrance , Soviet occupation between 1939 and 1941 resulted in the death of 150 , 000 and deportation of 320 , 000 of Polish citizens , when all who were deemed dangerous to the Soviet regime were subject to sovietization , forced resettlement , imprisonment in labor camp s ( the " Gulags " ) or murdered , like the Polish officers in the Katyn massacre . Misconceptions . There are several common misconceptions regarding the Polish September Campaign .