French Collapse in 1940
The French had been traumatized by WWI and by the devastation suffered by the parts of their country that were fought over. So they devised a plan to avoid repetition: the Maginot Line would secure the Franco-German border to the south, while the bulk of the mobile French army was stationed in the north, tasked with advancing into Belgium soon as the Germans attacked, to fight as far forward and outside of France as possible.
The French had adequately fortified the south, and amassed enough mobile forces in the north to keep the Germans from bursting into France via that route. However, they ignored a stretch of wooded terrain in the center, the Ardennes Forrest, which they deemed impassable for tanks, and so kept it lightly defended. The Germans figured the Ardennes was actually passable, so they massed the bulk of their armor against that sector.
When the Germans burst through the Ardennes and raced to the English Channel to sever France’s armies in the north from the rest of the country, the French were caught wrong footed: their mobile forces were advancing into Belgium, and couldn’t be turned around in time to stop the Germans pouring out of the Ardennes, and they lacked adequate reserves to send in and plug the widening gap.
Collapse quickly followed, and the same country that two decades earlier had fought the Germans for four bloody years and emerged victorious in WWI, capitulated and signed a humiliating surrender after just 40 days’ fighting in WWII.
