Heinz Guderain - Inadequacies of French Leadership

Guderain explains how the French miscalculated during the war, ultimately causing their own downfall.

Tanks:
Tanks were proven in WWI to be a highly effective weapon, and their development in Germany was only stimulated by the international ban on German tank production.
The French, however, relied on sheer man- and firepower rather than the mobility that tanks provided, and overlooked them as effective weapons.

Military Strategy:
The French army was accustomed to making well-informed decisions according to a set plan, but this methodology was ill-suited to the sudden style of Blitzkrieg.
The French relied too much on permanent fortifications, such as the Maginot line, and so were not able to easily change military plans.
The French assumed that the German army would conduct an invasion exactly as they did in WWI with the Schlieffen plan, and were caught by surprise by Hitler's differing tactics.
The French failed to take advantage of the German's vulnerable position during their invasion of Poland.