Gauging a potential opponent’s military capability is a very inexact business. A simple counting of boots in the barracks can be extremely misleading. History is replete with instances of miscalculation and of cases where god was not on the side of the big battalions. Young Alexander of Macedon headed off east in 344 BCE and defeated the much larger Persian Empire, being rewarded with title Alexander the Great, and ultimate accolade of a retrospective virgin birth. Did he know the odds, and would it have made any difference?

Both Hitler and before him Napoleon headed off to Moscow with high hopes, and disastrous results. Napoleon himself put a finger on one of the key factors. What I want in general, he famously said, is that he is lucky. To which might be added the vagaries of fate, such as disease and weather. Moscow’s fierce winter might have been anticipated but the Mongols might reasonably have been taken unawares by the typhoons – the kamikaze or divine wind – that destroyed their invasion fleet off the coast of Japan in the 13^th century. With the precedent of Napoleon why did Hitler make the same mistake?