Why did Hitler’s imperial dreams take Stalin by surprise?

The most extraordinary thing, still, about Operation Barbarossa is the complete surprise the Wehrmacht achieved. In the early hours of 22 June 1941 the largest invasion force in history, ultimately some three million men, struck at the Soviet Union on a front of nearly 2,000 miles. When Stalin was woken with the news, he wouldn’t believe it. It couldn’t be Hitler’s doing, he insisted; surely just sabre-rattling by Wehrmacht generals? Hours passed before he would accept his calamitous misjudgments and issue a general order to fight back by every means.

Hitler’s strategic challenge in the late 1930s had been essentially the same as the Kaiser’s in 1914: how to make war simultaneously on two fronts. The Kaiser, thanks to a theoretical plan conceived 20 years earlier by the chief of the Grosser Generalstab, Alfred von Schlieffen, ‘solved’ the problem by tactics inspired by the Battle of Cannae, in which Hannibal annihilated a superior Roman army by encirclement, and Napoleon’s ‘strategy of the central position’, designed to defeat two cooperating armies by concentrating force against one of them till it yielded, then turning to face the other.