Seems to me like Crete was a pretty near-run thing. Most of the airfields were held by the Allies, the German paratroopers took heavy casualties, and the Royal Navy repulsed attempts to reinforce them by sea.

Results: Turkey enters war on Allied side sooner? Balkan front reopened? Yugoslavia given more aid? Greek Civil War averted? Towards the end of the war, if the Allies get further into the Balkans they might have made a case for aligning more than just Greece with the West.

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Sole founder of Encyc.org, now covering World War II.