<P> After British troops arrived in Greece in March 1941, British bombers operating from Greek bases could reach the Romanian oil fields, vital to the German war effort . Hitler decided that he had to help the Italians and committed German troops to invade Greece via Yugoslavia (where a coup had deposed the German - friendly government). </P> <P> On 6 April 1941, the Wehrmacht invasions of Yugoslavia (Operation 25) and Greece (Operation Marita) both started . Together with the rapid advance of the German forces the Italians attacked Yugoslavia in Dalmatia and pushed the Greeks finally out of Albania . On 17 April, Yugoslavia surrendered to the Germans and the Italians . On 30 April, Greece too surrendered to the Germans and Italians, and was divided into German, Italian and Bulgarian sectors . The invasions ended with a complete Axis victory in May when Crete fell . On 3 May, during the triumphal parade in Athens to celebrate the Axis victory, Mussolini started to boast of an Italian Mare Nostrum in the Mediterranean sea . </P> <P> Some 28 Italian divisions participated in the Balkan invasions . The coast of Yugoslavia was occupied by the Italian Army, while the rest of the country was divided between the Axis forces (a German and Italian puppet State of Croatia was created, under the nominal sovereignty of Prince Aimone, Duke of Aosta, but actually governed by the Croatian fascist Ante Pavelić). The Italians assumed control of most of Greece with their 11th Army, while the Bulgarians occupied the northern provinces and the Germans the strategically most important areas . Italian troops would occupy parts of Greece and Yugoslavia until the Italian armistice with the Allies in September 1943 . </P> <P> In spring 1941, Italy created a Montenegrin client state and annexed most of the Dalmatian coast as the Governorship of Dalmatia (Governatorato di Dalmazia). Yugoslav Partisans fought a guerilla war against the occupying forces until 1945 . </P>

When did italy join the allies in ww2