Writing from France for the Hearst papers in 1940, H.R. Knickerbocker (1898 – 1949) had witnessed the total collapse of the French Army. His 1941 book Is Tomorrow Hitler's? clearly summarized his reasoning as to why Nazi Germany was able to overwhelm the French and turn their withdraw into a route. These columns answer the question "Why did France fall?":
"Because the French people were hypnotized by their low birth rate; because their Maginot Line had imprisoned their army; because they had no Churchill to inspire and lead them ... their comparative lack of weapons would not have mattered... if they had had the spirit to win they could have held the Germans until the deficiency could be made up."
"Tanks cannot cross properly defended rivers, and there were several sets of rivers which the French could have held if they chose: the Meuse, the Somme and the Oise, the Aisne, the Marne, the Seine, and finally the Loire, but they held not at all at any of these natural barriers. At most of these rivers I was present during the retreat, and it astonished all of us to visit a French position along a river one day and observe how strong it was, and how difficult it would be to take, and then the next day to learn the Germans had taken it within a few hours of our departure."
The image above depicts captured French tanks rolling down a Paris boulevard with their new German crews.
More primary source articles about W.W. II France can be read here...
Click here to read about the German concept of Blitzkrieg.