The occupation of the Balkans
Between October 28, 1940 and June 1, 1941, the Axis powers occupied the Balkans. Hungary, Romania, and Bulgaria became allies of Germany and fully-fledged members of the Axis, while Yugoslavia and Greece opposed the occupation with the support of Britain. Together, the trio sent to about 50 divisions into the Balkans, of which 28 were Yugoslavs, 18 Greek, and 3 British. In theory, it was a tremendous force, but it was not properly coordinated, and was particularly weak in the air and armor, the main components of the "Blitzkrieg". Many of these forces were armed with World War I weapons and had a combat doctrine that was suited to the previous war. Only on the sea did the Allied forces have the advantage, and here, too, there were serious losses when ships were exposed to aircraft from coastal bases.
On October 28, 1940, Mussolini issued an ultimatum to Greece and at the beginning of November; an Italian army of 150,000 troops invaded it from Albania. This force encountered the stubborn resistance of a 75,000-strong Greek army that fought back and exploited the winter in this mountainous region, launched a counter-offensive defeating the Italian army and occupying southern Albania.
Germany, fearing the threat developing in Europe's southern hemisphere, decided to go to the aid of its Italian ally. On December 13, Hitler issued Order No. 20,-- Operation Marita following which he issued Order 22 supplementing it. In March, Yugoslavia was also persuaded to join the Axis countries, but immediately after the signing of the agreement with Germany, a coup was launched in Yugoslavia headed by General Simovich, which installed a government that supported the Allies. These events were too much for the Germans and so on the 6th April 1941 they launched a parallel offensive from Rumania, Bulgaria and Albania against Yugoslavia and Greece.
In the course of ten days, on 17 April, Yugoslavia surrendered to the German army under the command of Field Marshal List and on 21 April the Greek army surrendered as well. The British Army, which came to the aid of Greece under the command of General Maitland-Wilson and numbered 57,000 troops, began to retreat and evacuate its forces. This included the 6th Australian Division, the 2nd New Zealand Division, a British armored brigade, a Polish brigade, and a number of companies from the land Israel. It managed to evacuate about 43,000 soldiers. 27,000soldiers evacuated from Greece were deployed to defend Crete, with the 2nd New Zealand Division forming the central force on the island whose commander, General Freiberg holder of the Victoria Cross was appointed overall commander
On May 20, the Germans attacked Crete in the largest airborne operation in history. Within eight days, they had succeeded in defeating the British force, which was twice as large, albeit in heavy losses to the German paratroopers. The British began again the evacuation of their troops by sea, this time evacuating some15,000 soldiers The Germans captured some 13,000 British soldiers and about 5,000 Greek..
Thus, in a few weeks the Germans crushed Yugoslavia and Greece as well as the considerable British forces that came to their aid. In this campaign German overall superiority in the employment of combined forces stood out, especially in the use of air power as a decisive factor in overcoming the quantitative superiority of the Allies. The Allies fought fiercely, but the German "Blitzkieg" was far more effective than the Allied combat doctrine and their headquarters work that were more suited to the battlefields of the 1914-1918 war.
Yugoslavia, like France, was divided into two - Croatia, which became a Nazi satellite and occupied Serbia. Greece remained under German occupation until the end of World War II.