In March 1941, a major Italian counterattack failed, and Germany was forced to come to the aid of its ally. Operation Marita began on April 6, 1941, with German troops invading Greece through Bulgaria in an effort to secure its southern flank. The combined Greek and British Commonwealth forces fought back with great tenacity, but were vastly outnumbered and outgunned, and finally collapsed. Athens fell on April 27. However, the British managed to evacuate about 50,000 troops. The Greek campaign ended in a quick and complete German victory with the fall of Kalamata in the Peloponnese.
Some historians regard the German campaign in Greece as decisive in determining the course of World War II, maintaining that it fatally delayed the Axis invasion of the Soviet Union.