"For Hitler, the war is a turning point as he sits there in 1918, eyes swathed in bandages, hearing that Germany has lost the war.

"There are many key figures of the post-war period for which the war was a formative and deeply wonderful experience. It is not unusual that Hitler is regarded in these terms. He is absolutely mesmerized and appalled that this could have happened. And, really, his political career begins almost immediately as an attempt to find those responsible, the November criminals, for the stab in the back.

"Hitler is, more than anyone else perhaps, the architect of the theory that Germany loses the war at home. And so in many ways his political career is launched at that moment. And almost immediately in the very earliest speeches in 1919, he identifies Jews and Bolsheviks as the key culprits. So it is an extremely important moment for him personally.

"Strategically, though, the idea that in some way the Second World War is the First World War all over again is, I think, wrong because Hitler quite clearly saw the need to learn lessons from the mistakes of 1914.

"In Mein Kampf, he clearly distances himself from the objectives of the Germany of 1914.

"Hitler says we have to concentrate on Eastern Europe and not worry about colonies and not worry about the Western Front. All our efforts should be directed eastward. And, that's the conclusion that he draws most obviously from the war. And that of course is why when the war comes in 1939, it's a very, very different war indeed. It begins in the east and only later moves to the west of Europe after Poland and the other countries have been overrun."