The German attack

In April 1941, Hitler decided to come to the aid of his ally Mussolini, at the same time hoping to secure his rear in the Balkans in light of his attack on the Soviet Union. Besides, the new Greek government (that had succeeded Metaxas' Regime following the latter's death towards the end of January 1941) had accepted Britain's offer for the dispatch of military aid. Metaxas himself had appeared hesitant towards the English in his efforts not to provoke German intervention against Greece, as he felt the proffered English forces would be insufficient to form an effective defence. The Germans had by now a pretext to intervene.
Passing on the one hand through Yugoslavia, where they had crushed the Yugoslav resistance, and on the other through Bulgaria - an ally of the Axis - the Germans invaded the country on 6 April 1941 and surrounded the Greek forces that were defending the Macedonian fortresses along the frontier in company with a small British campaign force of Australian and New Zealand soldiers. The military leadership surrendered on 23 April. Before the German advance,
the King and the government, along with the Bristish forces fighting beside the Greeks, had transferred to the still-free Crete, where the last act of the war was played out.
On 20 May, the German attack began and met with a vigorous resistance, despite the insufficient defensive organization of the island. Greek, English, Australian and New Zealand soldiers, as well as armed civilians, were lying in wait for the enemy at the spots where the landing was anticipated and decimated it. Only the next day did the Germans manage, with difficulty, to land. There began a series of tough battles with the defenders who retreated step by step, fighting stubbornly, until the enemy's superiority in arms eventually overwhelmed them.
With the occupation of Crete at the end of May, Greece passed fully into German hands while the King and the government fled to settle in Cairo, Egypt, along with the remnants of the Greek forces. Crete paid a heavy toll in reprisals especially for the decimation of the crack German parachutists. It is worth noting that the ten-day operation cost the Germans more casualties than any they took during the whole operation against Yugoslavia and Greece.