Balkan Campaign ( World War II ) The Balkan Campaign of World War II began with the Italian invasion of Greece on 28 October 1940 . In the early months of 1941 , Italy ' s offensive had been stalled and a Greek counter - offensive pushed into Albania . Germany sought , by deploying troops to Romania and Bulgaria , to aid Italy by attacking Greece from the east ; while the British landed troops and aircraft to shore up Greek defences . A " coup d ' état " in Yugoslavia on 27 March caused Hitler to order the conquest of that country . The invasion of Yugoslavia by Germany and Italy began on 6 April , simultaneously with the new Battle of Greece . On 11 April , Hungary joined the invasion . By 17 April the Yugoslavs had signed an armistice and by 30 April all of mainland Greece was under German or Italian control . On 20 May Germany invaded Crete by air and by 1 June all remaining Greek and British forces on the island had surrendered . Although it had not participated in the attacks of the April , Bulgaria occupied parts of both Yugoslavia and Greece shortly after and for the remainder of the war in the Balkans . Background . After World War I , with the complete collapse of the Ottoman Empire and the Austro - Hungarian Empire , the Albanians looked to the Kingdom of Italy for protection against its enemies . In 1919 , Albania ' s territorial integrity was confirmed at the Paris Peace Conference after United States President Woodrow Wilson opposed a plan by the European powers to divide Albania amongst its neighbors . There were attempted backroom negotiations that ultimately failed . However , after 1925 , Italian dictator Benito Mussolini sought to dominate Albania . In 1928 , Albania became a kingdom under Zog I . Zog was a clan chief and former Prime Minister . Zog failed to stave off Italian ascendancy in Albanian internal affairs . On 7 April 1939 , Mussolini ' s troops occupied Albania , overthrew Zog , and annexed the country to the Italian Empire . Campaign . Greco - Italian War . The Greco - Italian War lasted from 28 October 1940 to 30 April 1941 and was part of World War II . Italian forces invaded Greece and made limited gains . But soon the Greeks counter - attacked and the Italians were repulsed and driven back into Albania . The Italians spent much of the winter stabilizing a line which left them in control of only about two - thirds of Albania . A much anticipated Italian offensive in March 1941 failed to make sufficient progress . Germany intervened in April and invaded Greece after a successful invasion of Yugoslavia . Invasion of Yugoslavia . The invasion of Yugoslavia ( also known as " Operation 25 " ) began on 6 April 1941 and ended with the unconditional surrender of the Royal Yugoslav Army on 17 April . The invading Axis powers ( Nazi Germany , Fascist Italy , Hungary , and Bulgaria ) occupied and dismembered the Kingdom of Yugoslavia . By cobbling together Bosnia and Herzegovina , some parts of Croatia , and Syrmia , the " Independent State of Croatia " ( " Nezavisna Država Hrvatska " , NDH ) was created by Germany and Italy . In some of the territory of the former Kingdom of Serbia and the Banat , the German - occupied Territory of the Military Commander in Serbia , the Germans appointed a puppet government , the Government of National Salvation led by Milan Nedić . In Montenegro , a puppet " Independent State of Montenegro " was created as an Italian protectorate . However , the " protectorate " was nominally a kingdom even though Prince Michael of Montenegro never accepted the crown . Battle of Greece . Hitler began planning to invade Greece in November 1940 , after the British occupied Crete and Lemnos . He ordered the German Invasion of Greece — code - named " Unternehmen Marita " ( " Operation Marita " ) by Germany — on 13 December 1940 for execution in March 1941 . The stated aim of the operation was to prevent the British from getting air bases within striking range of the Romanian oilfields . On 6 April 1941 , the German Army invaded northern Greece , while other elements launched an attack against Yugoslavia . Breaking through the Yugoslav lines in southern Yugoslavia allowed Germany to send reinforcements to the battlefields of northern Greece . The German army out - flanked the Greek Metaxas Line fortifications and , despite the assistance provided by a British expeditionary corps , set out to capture the southern Greek cities . The Battle of Greece ended with the German entry into Athens and the capture of the Peloponnese , although about 40 , 000 Allied soldiers were evacuated to Crete , prompting one of the largest airborne attacks in the history of warfare : Operation Merkur , or the Battle of Crete . Battle of Crete . On 20 May 1941 , German paratroopers were dropped over the airfields of northern Crete to occupy the island . They were met by heavy resistance from Allied forces and the local Cretan population but eventually the defenders were overwhelmed by the tactically superior German forces . The British Government ordered an evacuation on 27 May and the remaining forces surrendered on 1 June . However , the heavy losses incurred by the paratroopers forced the Supreme Command of the Wehrmacht to abandon large - scale airborne operations for the remainder of the war . Result . By 1 June 1941 , all of Albania , Yugoslavia and Greece were under Axis control . Greece was placed under triple occupation , and Yugoslavia was dissolved and occupied . Germany had gained a significant strategic advantage : direct access to the Mediterranean . The Allied High Command feared that Crete and Greece would be used as " springboard " for an invasion of British Egypt or Cyprus . However , any plans for a large - scale invasion of Egypt and Palestine were abandoned when Operation Barbarossa commenced on 22 June . The effect of the Balkans Campaign on the outcome of Operation Barbarossa is still debated to this day . Bulgarian occupation . On 6 April 1941 , despite having officially joined the Axis Powers , the Bulgaria n government did not participate in the invasion of Yugoslavia and the Battle of Greece . As German , Italian , and Hungarian troops crushed Yugoslavia and Greece , the Bulgarians remained on the side - lines . The Yugoslav government surrendered on 17 April . The Greek government was to hold out until 30 April . On 20 April , the Bulgarian Army occupied most of Western Thrace and the Greek province of Eastern Macedonia , which had been already conquered by Germany , with the goal of restoring its pre - World War I outlet to the Aegean Sea . Bulgarian troops also occupied and much of eastern Serbia , where the so - called Vardar Banovina was divided between Bulgaria and the Italians . Resistance movements . Throughout the remainder of the war , active Yugoslav , Greek , and Albanian resistance movements forced Germany and its allies to garrison hundreds of thousands of soldiers permanently in the three countries , denying them to the other fronts . Especially in Yugoslavia after 1943 , the threat of an Allied invasion and the activities of the partisans necessitated large - scale counter - insurgency operations , involving several divisions , including elite Mountain Infantry ( " Gebirgsjäger " ) units .