A combination of El Alamein and Stalingrad. The El Alamein just as the Germans were pushing into Stalingrad, meaning troops had to be diverted from the Eastern Front to the North African Theatre.
The Battle of Moscow also gave the Russians time to rebuild their defences and armies, so it too has a very strong case. America was already giving huge amounts of aid to Britain and the Soviet Union when Pearl Harbour happened, and may well have entered the war against Germany at a later date even if Pearl Harbour had never happened. Hitler was also planning further invasions of Britain after the Battle of Britain, but it was certainly a useful delay.
At the risk of sounding like a post-documentary advertisement, if you want to find probably the best history book written about WW2, and the links between all the various theatres of war, then I'd recommend 'A World At Arms' by Gerhard L. Weinberg. It's extremely informative and reveals a hell of a lot of stuff that you generally would have no idea about.
The Battle of Moscow also gave the Russians time to rebuild their defences and armies, so it too has a very strong case. America was already giving huge amounts of aid to Britain and the Soviet Union when Pearl Harbour happened, and may well have entered the war against Germany at a later date even if Pearl Harbour had never happened. Hitler was also planning further invasions of Britain after the Battle of Britain, but it was certainly a useful delay.
At the risk of sounding like a post-documentary advertisement, if you want to find probably the best history book written about WW2, and the links between all the various theatres of war, then I'd recommend 'A World At Arms' by Gerhard L. Weinberg. It's extremely informative and reveals a hell of a lot of stuff that you generally would have no idea about.