Soviet – Japanese War ( 1945 ) The Soviet - Japanese War of 1945 ( , lit . Soviet - Japanese War ) , began on August 9 , 1945 , with the Soviet invasion of the Japanese puppet state of Manchukuo . The Soviets terminated Japanese control of Manchukuo , Mengjiang ( inner Mongolia ) , northern Korea , southern Sakhalin , and the Kuril Islands . The rapid defeat of Japan ' s Kwantung Army was a significant factor in the Japanese surrender and the termination of World War II . Summary . At the Tehran Conference ( November 1943 ) , Stalin agreed that the Soviet Union would enter the war against Japan once Nazi Germany was defeated . At the Yalta Conference ( February 1945 ) , Stalin agreed to Allied pleas to enter World War II ' s Pacific Theater within three months of the end of the war in Europe . The invasion began on August 8 , 1945 , precisely three months after the German surrender on May 8 ( May 9 , 0 : 43 Moscow time ) . The commencement of the invasion fell between the atomic bombings of Hiroshima , on August 6 , and Nagasaki , on August 9 . Although Soviet leader Joseph Stalin had not been told much detail of the Western Allies ' atomic bomb program by Allied governments , he was nonetheless well aware of its existence and purpose by means of Soviet intelligence sources . However , by virtue of the timing of the agreements at Tehran and Yalta , and the long term buildup of Soviet forces in the Far East since Tehran , it is clear that news of the attacks on the two cities played no major role in the timing of the Soviet invasion ; the date of the invasion was foreshadowed by the Yalta agreement , the date of the German surrender , and the fact that on August 3 , Marshal Vasilevsky reported to Stalin that , if necessary , he could attack on the morning of August 5 . Furthermore , while Stalin could reasonably have concluded that an atomic bombing of Japan was imminent , it does not appear he was overly impressed with the atomic bomb ' s potential , certainly not so much so as to think it might compel a nation as averse to surrender as Japan into an earlier capitulation . At 11pm Trans - Baikal time on August 8 , 1945 , Soviet foreign minister Molotov informed Japanese ambassador Sato that the Soviet Union had declared war on the Empire of Japan , and that from August 9 the Soviet Government would consider itself to be at war with Japan . At one minute past midnight Trans - Baikal time on August 9 , 1945 , the Soviets commenced their invasion simultaneously on three fronts to the east , west and north of Manchuria . The operation was subdivided into smaller operational and tactical parts : and subsequently Though the battle extended beyond the borders traditionally known as " Manchuria " — that is , the traditional lands of the Manchus — the coordinated and integrated invasions of Japan ' s northern territories has also been called " the Battle of Manchuria " . Since 1983 , the operation has sometimes been called Operation August Storm , after American Army historian LTC David Glantz used this title for a paper on the subject . It has also been referred to by its Soviet name , the " Manchurian Strategic Offensive Operation " , however this name refers more to the Soviet invasion of Manchuria ( 1945 ) than to the whole war . This offensive should not be confused with the Soviet - Japanese Border Wars , ( particularly the Battle of Khalkhin Gol / Nomonhan Incident of May – September 1939 ) , that ended in Japan ' s defeat in 1939 , and led to the Soviet – Japanese Neutrality Pact . Background and buildup . The Russo - Japanese War of the early 20th century resulted in a Japanese victory and the Treaty of Portsmouth by which , in conjunction with other later events including the Mukden Incident and Japanese invasion of Manchuria in September 1931 , Japan eventually gained control of Korea , Manchuria and Southern Sakhalin . In the late 1930s there were a number of Soviet - Japanese border incidents , the most significant being the Battle of Lake Khasan ( Changkufeng Incident , July – August 1938 ) and the Battle of Khalkhin Gol ( Nomonhan Incident , May – September 1939 ) , which led to the Soviet – Japanese Neutrality Pact of April 1941 . The Neutrality Pact freed up forces from the border incidents and enabled the Soviets to concentrate on their war with Germany , and the Japanese to concentrate on their southern expansion into Asia and the Pacific Ocean . However , with success at Stalingrad , and the eventual defeat of Germany becoming increasingly certain , the Soviet attitude to Japan changed , both publicly , with Stalin making speeches denouncing Japan , and " privately " , with the Soviets building up forces and supplies in the Far East . At the Tehran Conference ( November 1943 ) , amongst other things , Churchill , Roosevelt and Stalin agreed that the Soviet Union would enter the war against Japan once Nazi Germany was defeated . However , Stalin faced a dilemma - he wanted to avoid a two - front war at almost any cost yet the Soviet leader also wanted to extract gains in the Far East as well as Europe . The only way Stalin could make Far Eastern gains without a two - front war would be for Germany to capitulate before Japan . Due to the Soviet - Japanese Neutrality Act , the Soviets made it policy to intern Allied aircrews who landed in Soviet territory following operations against Japan , although airmen held in the Soviet Union under such circumstances were usually allowed to " escape " after some period of time . Nevertheless , even before the defeat of Germany the Soviet buildup in the Far East steadily accelerated . By early 1945 it had become apparent to the Japanese that the Soviets were preparing to invade Manchuria , though they were unlikely to attack prior to Germany ' s defeat . In addition to their problems in the Pacific , the Japanese realised they needed to determine when and where a Soviet invasion would occur . At the Yalta Conference ( February 1945 ) , amongst other things , Stalin secured from Roosevelt the promise of Stalin ' s Far Eastern territorial desires , in return agreeing to enter the Pacific war within two or three months of the defeat of Germany . By the middle of March 1945 , things were not going well in the Pacific for the Japanese , and they withdrew their elite troops from Manchuria to support actions in the Pacific . Meanwhile the Soviets continued their Far Eastern buildup . The Soviets had decided that they did not wish to renew the Neutrality Pact . The terms of the Neutrality Pact required that 12 months before its expiry , the Soviets must advise the Japanese of this , so on 5 April 1945 they informed the Japanese that they did not wish to renew the treaty . This caused the Japanese considerable concern , but the Soviets went to great efforts to assure the Japanese that the treaty would still be in force for another twelve months , and that the Japanese had nothing to worry about . On 9 May 1945 ( Moscow time ) , Germany surrendered , meaning that if the Soviets were to honour the Yalta agreement , they would need to enter war with Japan by 9 August 1945 . The situation continued to deteriorate for the Japanese , and they were now the only Axis power left in the war . They were keen to remain at peace with the Soviets and extend the Neutrality Pact , and they were also keen to achieve an end to the war . Continuously since Yalta they had repeatedly approached , or tried to approach , the Soviets in order to extend the neutrality pact , and to enlist the Soviets in negotiating peace with the allies . The Soviets did nothing to discourage these Japanese hopes , and drew the process out as long as possible ( whilst continuing to prepare their invasion forces . ) One of the roles of the Cabinet of Admiral Baron Suzuki , which took office in April 1945 , was to try to secure any peace terms short of unconditional surrender . In late June they approached the Soviets , ( the Neutrality Pact was still in place ) , inviting them to negotiate peace with the allies in support of Japan , providing them with specific proposals and in return they offered the Soviets very attractive territorial concessions . Stalin expressed interest , and the Japanese awaited the Soviet response . The Soviets continued to avoid providing a response . The Potsdam Conference was held from 16 July to 2 August 1945 . On 24 July the Soviet Union recalled all embassy staff and families from Japan . On 26 July the conference produced the Potsdam Declaration whereby Churchill , Truman and Chiang Kai - shek ( the Soviet Union was not at war with Japan ) demanded the unconditional surrender of Japan . The Japanese continued to wait for the Soviet response , and avoided responding to the declaration . The Japanese had been monitoring Trans - Siberian Railway traffic and Soviet activity to the east of Manchuria and in conjunction with the Soviet delaying tactics , this suggested to them that the Soviets would not be ready to invade east Manchuria before the end of August . They did not , however , have any real idea , and no confirming evidence , as to when or where any invasion would occur . The Japanese were caught completely by surprise when the Soviets declared war an hour before midnight on 8 August 1945 , and invaded simultaneously on three fronts just after midnight on 9 August . Combatant forces . Soviets . The Far East Command , under Marshal of the Soviet Union Aleksandr Vasilevsky , had a plan for the conquest of Manchuria that was simple but huge in scale , calling for a massive pincer movement over all of Manchuria . This pincer movement was to be performed by the Transbaikal Front from the west and by the 1st Far East Front from the east ; the 2nd Far East Front was to attack the center of the pocket from the north . The only Soviet equivalent of a theater command that operated during the war ( apart from the short - lived 1941 " Directions " in the west ) , Far East Command , consisted of three Red Army front s . The Transbaikal Front , under Marshal R . Y . Malinovsky , was to form the western half of the Soviet pincer movement , attacking across the Inner Mongolian desert and over the Greater Khingan mountains . These forces had the objective to secure Mukden ( present day Shenyang ) , then meet troops of the 1st Far East Front at the Changchun area in south central Manchuria , and in doing so finish the double envelopment . The 1st Far East Front , under Marshal K . A . Meretskov , was to form the eastern half of the pincer movement . This attack involved striking towards Mudanjiang ( or Mutanchiang ) , and once that city was captured , the force was to advance towards the cities of Jilin ( or Kirin ) , Changchun and Harbin . Its final objective was to link up with forces of the Trans - Baikal Front at Changchun and Jilin ( or Kirin ) thus closing the double envelopment movement . As a secondary objective , the 1st Far East Front was to prevent Japanese forces from escaping to Korea , and then invade the Korean peninsula up to the 38th parallel , establishing in the process what later became North Korea . The 2nd Far East Front , under General M . A . Purkayev , was in a supporting attack role . Its objectives were the cities of Harbin and Tsitsihar , and the prevention of an orderly withdrawal to the south by the Japanese forces . Once troops from the 1st Far East Front and Trans - Baikal Front captured the city of Changchun , the 2nd Far East Front were to attack the Liaotung Peninsula and seize Port Arthur ( present day Lüshun ) . Each Front had " front units " attached directly to the Front instead of an army . The forces totaled 89 division s with 1 . 5 million men , 3 , 704 tank s , 1 , 852 self propelled gun s , 85 , 819 vehicles and 3 , 721 aircraft . Approximately one - third of its strength was in combat support and services . Its naval forces contained 12 major surface combatants , 78 submarines , numerous amphibious craft , and the Amur river flotilla , consisting of gunboats and numerous small craft . The Soviet plan incorporated all the experience in maneuver warfare that the Soviets had acquired fighting the Germans . Japanese . The Kwantung Army of the Imperial Japanese Army , under General Otsuzo Yamada , was the major part of the Japanese occupation forces in Manchuria and Korea , and consisted of two Area Armies ( the First Area Army ( northeastern Manchukuo ) and the Third Area Army ( southwestern Manchukuo ) ) , and three independent armies ( responsible for northern Manchuria , North Korea , Mengjiang , South Sakhalin and the Kurils ) . Each Area Army ( " Homen Gun " , the equivalent of a Western " army " ) had headquarters units and units attached directly to the Area Army , in addition to the field armies ( the equivalent of a Western corps ) . In addition to the Japanese , there was the forty - thousand - strong Manchukuo Defense Force , composed of eight under - strength , poorly equipped , poorly trained Manchukuoan divisions . The Kwantung Army had over six hundred thousand men in twenty - five divisions ( including two tank divisions ) and six Independent Mixed Brigade s . These contained over 1 , 215 armored vehicles ( mostly armored cars and light tanks ) , 6 , 700 artillery pieces ( mostly light ) , and 1 , 800 aircraft ( mostly trainers and obsolete types ; they only had 50 first line aircraft ) . The Imperial Japanese Navy contributed nothing to the defense of Manchuria , the occupation of which it had always opposed on strategic grounds . On economic grounds , Manchuria was worth defending since it had the bulk of usable industry and raw materials outside of Japan and was still under Japanese control in 1945 . However , the Japanese forces ( Kwantung Army ) were far below authorized strength ; most of their heavy military equipment and all of their best military units had been transferred to the Pacific front over the previous three years . By 1945 , the Kwantung Army contained a large number of raw recruits . As a result , the Kwantung Army had essentially been reduced to a light infantry counter - insurgency force with limited mobility and experience . On paper , the Japanese forces were no match for the highly mobile mechanized Red Army , with its vastly superior tanks , artillery , experience and tactics . Compounding the problem , the Japanese military made many wrong assumptions and major mistakes , the two most significant being : Due to the withdrawal of the Kwantung Army ' s elite forces for redeployment into the Pacific Theatre , new operational plans for the defence of Manchuria against a seemingly inevitable Soviet attack were made by the Japanese in the summer of 1945 . These called for the redeployment of the majority of forces from the border areas ; the borders were to be held lightly and delaying actions fought while the main force was to hold the southeastern corner in strength ( so defending Korea from attack ) . Further , they had only observed Soviet activity on the Trans - Siberian railway and along the east Manchurian front , and so were preparing for an invasion from the east . They believed that when an attack occurred from the west , the redeployed forces would be able to deal with it . However , although this redeployment had been initiated , it was not due to be completed until September , and hence the Kwantung Army were in the middle of redeployment when the Soviets launched their attack simultaneously on all three fronts . Campaign . The operation was carried out as a classic double pincer movement over an area the size of Western Europe . In the western pincer , the Red Army advanced over the deserts and mountains from Mongolia , far from their resupply railways . This confounded the Japanese military analysis of Soviet logistics , and the defenders were caught by surprise in unfortified positions . The Kwantung Army commanders were involved in a planning exercise at the time of the invasion , and were away from their forces for the first eighteen hours of conflict . Communication infrastructure was poor , and communication was lost with forward units very early on . However , the Kwantung Army had a formidable reputation as fierce and relentless fighters , and even though understrength and unprepared , put up strong resistance at the town of Hailar which tied down some of the Soviet forces . At the same time , Soviet airborne units were used to seize airfields and city centers in advance of the land forces , and to ferry fuel to those units that had outrun their supply lines . The Soviet pincer from the east crossed the Ussuri and advanced around Khanka Lake and attacked towards Suifenhe , and although Japanese defenders fought hard and provided strong resistance , the Soviets proved overwhelming . Perhaps the most glaring fact illustrating the differences in efficacy between the two opponents was that , often , the speed of Soviet advances far outpaced any sort of fighting withdrawal the Japanese could conduct , which formed a crucial element of the entire Japanese strategy for defending the Manchurian heartland . After a week of fighting , during which Soviet forces had penetrated deep into Manchukuo , Japan ' s Emperor Hirohito recorded the Gyokuon - hōsō which was broadcast on radio to the Japanese nation on August 15 , 1945 . The idea of surrender was incomprehensible to the Japanese people , and combined with Hirohito ' s use of formal and archaic language , the fact that he did not use the actual word " surrender " , the poor quality of the broadcast , and poor lines of communication , there was some confusion amongst the Japanese about what the announcement actually meant . The Imperial Japanese Army Headquarters did not immediately communicate the cease - fire order to the Kwantung Army , and many elements of the army either did not understand it , or ignored it . Hence , pockets of fierce resistance from the Kwantung Army continued , and the Soviets continued their advance , largely avoiding the pockets of resistance , reaching Mukden , Changchun and Qiqihar by August 20 . On the Soviet right flank , the Soviet - Mongolian Cavalry - Mechanized Group had entered Inner Mongolia and quickly took Dolon Nur and Kalgan . The Emperor of Manchukuo ( and former Emperor of China ) , Puyi , was captured by the Soviet Red Army . The cease - fire order was eventually communicated to the Kwantung Army , but not before the Soviets had made most of their territorial gains . On August 18 , several Soviet amphibious landings had been conducted ahead of the land advance : three in northern Korea , one in Sakhalin , and one in the Kuril Islands . This meant that , in Korea at least , there were already Soviet soldiers waiting for the troops coming overland . In Sakhalin and the Kurils , it meant a sudden and undeniable establishment of Soviet sovereignty . The land advance was stopped a good distance short of the Yalu River , the beginning of the Korean peninsula , when even the aerial supply lines became unavailable . The forces already in Korea were able to establish a bit of control in the peninsula ' s north , but the ambition to take the entire peninsula was cut short when American forces landed at Incheon on September 8 , six days after the signing of the Japanese Instrument of Surrender . Importance and consequences . From the time of the first major Japanese military defeats in the Pacific , the non - military leaders of Japan had come to realise that the Japanese military campaign was economically unsustainable , and there were a number of initiatives to negotiate a cessation of hostilities and the consolidation of Japanese territorial and economic gains . Hence , elements of the non - military leadership had first made the decision to surrender as early as 1943 ; the major issue was the terms and conditions of surrender , not the issue of surrender itself . For a variety of diverse reasons , none of the initiatives were successful , the two major reasons being the Soviet Union ' s deception and delaying tactics , and the attitudes of the " Big Six " , the powerful Japanese military leaders . " ( Refer to Surrender of Japan for more detail . ) " The Manchurian Strategic Offensive Operation , along with the atomic bombings of Hiroshima and Nagasaki , combined to break the Japanese political deadlock and force the Japanese leaders to accept the terms of surrender demanded by the allies . In the " Sixty years after Hiroshima " issue of the Weekly Standard , American historian Richard B . Frank points out that there are a number of schools of thought with varying opinions of what caused the Japanese to surrender . He describes what he calls the " traditionalist " view , which asserts that the Japanese surrendered because the Americans dropped the atomic bombs . He goes on to summarise other points of view . Tsuyoshi Hasegawa ' s research has led him to conclude that the atomic bombings were not the principal reason for Japan ' s capitulation . He argues that Japan ' s leaders were impacted more by the swift and devastating Soviet victories on the mainland in the week following Joseph Stalin ' s August 8 declaration of war because the Japanese strategy to protect the home islands was designed to fend off a US invasion from the South , and left virtually no spare troops to counter a Soviet threat from the North . This , according to Hasegawa , amounted to a " strategic bankruptcy " for the Japanese and forced their message of surrender on August 15 , 1945 . Others with similar views include The " Battlefield " series documentary , Drea , Hayashi , and numerous others , though all , including Hasegawa , state that the surrender was not due to any single factor or single event . The Soviet invasion and occupation of the defunct " Manchukuo " marked the start of a traumatic period for the more - than - one - million occupants of the puppet state who were of Japanese descent . The situation for the Japanese military occupants was clear , but the Japanese colonists who had made " Manchukuo " their home , particularly those born in " Manchukuo " , were now stateless and homeless , and the ( non - Japanese ) Manchurians wanted to be rid of these foreigners . Many were killed , many others ended up in Siberian prisons for up to 20 years , and some made their way to the Japanese home islands , where they were also treated as foreigners . Manchuria was " cleansed " by Soviet forces of any potential military resistance . With Soviet support for the spread of Communism , Manchuria provided the main base of operations for Mao Zedong ' s forces , who proved victorious in the following four years of the Chinese Civil War . These military successes in Manchuria and China by the Communist Chinese led to the Soviet Union giving up their rights to bases in China — promised by the Western Allies — because all of the deemed - by - the - Soviets - to - be - " Chinese " - land which had been gained by the Soviets , ( as distinct from what the Soviets considered to be " Soviet " - land - which - had - been - occupied - by - the - Japanese ) , was eventually turned over to the People ' s Republic of China . Note , however , that before leaving Manchuria , Soviet forces and bureaucracy dismantled almost all of the portable parts of the considerable Japanese built industry in Manchuria and relocated it to " restore industry in war - torn Soviet territory " . That which was not portable was either disabled or destroyed ; the Soviets had no desire for Manchuria to be an economic rival , particularly to the underdeveloped Far Eastern Soviet Territories . As agreed at Yalta , the Soviet Union had intervened in the war with Japan within three months of the German surrender , and they were therefore entitled to the territories of Sakhalin and the Kuril Islands and also to preeminent interests over Port Arthur and Dalian , with its strategic rail connections . The territories on the Asian mainland were subsequently transferred to the full control of the People ' s Republic of China in 1955 ; the other possessions are still administered by the Soviet Union ' s successor state , Russia . Though the north of the Korean peninsula was under Soviet control , the logistic machine driving the Soviet invasion forces had given out before the entire peninsula could be seized . With the American landing at Incheon — some time before the Red Army could have remobilized and secured the entire peninsula — Korea was effectively divided . This was a precursor to the Korean War five years later . Further reading . All are in English : Japanese Monographs . The " Japanese Monographs " and the " Japanese Studies on Manchuria " - The 187 Japan Monographs are a series of operational histories written by former officers of the Japanese army and navy under the direction of General Headquarters of the U . S . Far East Command .