you simplify it.
1914-1918 most of the western front battles were fought on french soil - they lost more men in WWI than America has lost in all of her wars.
1940 their military leadership was still stuck in WWI - they imagined they were safe behind the Maginot line. When it failed, they floundered. The men fought, but the generals gave up hope early - probably broken from Verdun 24 years earlier.
“you simplify it.”
I don’t know. It’s pretty hard to explain away the continent’s largest modern army being defeated in six weeks and their nation occupied in humiliation.
The French military under Napoleon was formidable for about a dozen years, but it was pretty crappy before and since. Hell, it even lost to Mexico (granted, it was a half-assed effort to begin with, and totally inept in its execution; though there was one French garrison that fought bravely, to its credit).