I read Shirer's Berlin Diary and Rise & Fall of the 3rd Reich several years ago. Shirer's explanation for why France fell to the Nazis so soon has the ring of truth to me more than others, but I'm one of these amateurs who has read a few books rather than some people in here with proper expertise.

IIRC he acknowledges some practical matters like the Maginot line not being long enough when Belgium fell and Nazis could go around it, forests that France did not think tanks could get thru, but German tanks had improved. Gas stations on main roads = tanks have fuel nearby unlike 1918. OK. That's certainly part of it. He spends much more time and ink on cultural rot. He characterized the French military as half sympathetic with communists/Stalin [still Hitler's ally] and half sympathetic with fascism. He also mentioned that the French military upper management was a bit of a gerontocracy. The typical French general, or a realistic characterization, was 75 years old and still had a grudge about grievances his grandfather, also a general, had against the English from the 19th Century. Meanwhile, the typical Nazi general was in his upper 40's, physically fit, got there on merit and hard work, ate the same food as his men, and had less of a feudal nobleman aristocrat vs. a sullen peasant relationship with his fighting men than the French.

Shirer is a journalist writing history and not a tenure-track historian, but he was there and tells a good story. My spidey sense is that this cultural type of reason is (1) difficult to measure and directly observe, (2) no longer fashionable after 7 decades of red scares among academics and knee-jerk pro and anti political correctness. Counting tanks and recording the average age of generals is more concrete, so we are inclined to give it more weight, but my gut says Shirer is onto something.

Anyhoo, France & WW2 has been addressed lots of times here, but please address Shirer's take on it if possible.