LAURENCE REES: And then shortly afterwards the Germans invade France, and this is a victory that has a devastating impact on the war - and on Stalin - doesn't it? 

SIMON SEBAG-MONTEFIORE: Yes. No one predicted it, because of course the French hadn’t collapsed under terrific pressure in World War One, and that’s the example everyone was thinking of. We now think of France as disastrous militarily, 'surrender monkeys' and all that, but in fact they’d withstood amazing pressure and a hell of a punishment in World War One. So with their colossal army no one thought that it would happen the way it did. Even Hitler was amazed by it, so it’s not surprising that all the other players were. For Stalin it was a total disaster, it changed everything. It turned what was a ruthless but perfectly sensible expedient decision to go into business with Hitler, to ally with Germany, to divide up Eastern Europe, it turned that into a complete disaster and the policy instantly became irrelevant really and a big mistake. Stalin’s personal reaction was collapse; he just couldn’t believe it. He was walking up and down all night just saying how could the French collapse like this? It made a mockery of his policy. But, thank God, England still survived. And, again, he thought that unless England was defeated Hitler would not risk a second front, and according to Bismarckian principles Germany would never risk a war on two fronts.

So he was still just about safe, but of course the old policy should have been obsolete by then - if not openly then secretly. Of course things did happen then, and there were stages in the dissolution of that policy before Stalin’s loyalty to it became absurd. It’s easy now to say he looked ridiculous, but in fact it was really the last two or three months before Barbarossa that he really became absurd. Before then there was still doubts and ways that the policy could be made to last, he believed, and I think that he wasn’t completely mad in thinking that.