13 May 1940, Sedan. German tanks have come through the Ardennes, the forest the French staff had judged too thick for armour, and are crossing the Meuse under a sky full of dive-bombers. Six weeks later a republic that thought it had the best army in Europe signs an armistice.
Why then
France built the Maginot Line to fight the last war and moved its best armies into Belgium to meet the attack it expected. The German plan, a 'sickle cut', went through the gap behind them. Radios in every tank, and aircraft working with the ground, turn a gamble into a rout.
What they wanted
Hitler needs France broken before Britain can rearm. Gamelin, the French commander, plans a Belgian battle like 1914 with better maps. Ordinary French soldiers expected the war to wait behind concrete.
What changed
338,000 British and French soldiers escape from Dunkirk; their equipment does not. Pétain's government signs the armistice and runs a collaborating state from the spa town of Vichy. On the BBC an unknown general, de Gaulle, tells the French that the flame of resistance must not go out.
Still argued
Marc Bloch, a historian who fought in 1940, blamed his own country's generals and society that same summer. Ernest May later found a German gamble that could easily have failed, against Allied staffs who misread what they knew.