Ian Kershaw is more nuanced. Rather than pointing at a single event, he lists a number of major decisions by the Axis powers that all affected the outcome of the war in such a way, that had they´ve been different; Germany would have had a good or near certain chance of winning the Second World War.

He lists;

• Great Britain's decision to fight on
• Germany's attack on the Soviet Union
• Japan decision to use the war between Germany and the Soviet Union by securing South East Asia.
• Mussolini's decision to invade Greece
• Roosevelts decision decision to send aid to Britain
• Roosevelts decision to wage undeclared war
• Japans decision to go to war
• Hitlers decision to declare war on the US

All of these decisions took place between May 1940 till the end of 1941 though, suggesting that the Second World War was decided within that period.