France suffered in World War I more than any other Western combatant. Most of the fighting on the Western Front took place on her soil, and she lost millions of men in trench warfare.
At Versailles in 1919 she was determined to never allow German aggression to threaten her again. She hoped that the combination of demilitarization, reparation, and occupation would force the Germans to abandon any hopes of invading France again.
In the 1920’s and 1930’s the French had the largest, most powerful army on the face of the earth. Much of their equipment was good, and they had large resources in their colonies upon which to draw. Both the United States and Great Britain looked to France to secure peace on the European continent. Great Britain would secure the seas.
France did not lack the tools, only the will. Tired of fear and bloodshed, France did not wish to take on the role of World superpower. Economically and socially, she could not. Much of her coal and food production had become battlefields. The French public did not support commitments of troops overseas.
The French government, her army, and many of her citizens were transfixed by the war. France prepared to fight World War I, not World War II. André Maginot, the French Minister of War, advocated and built a series of fortifications all along the border with Germany. Named for their advocate, the Maginot Line was built to fight a war that was already over. Strong forts linked by tunnels and smaller redoubts provided a very tough defensive line. But by the thirties, static fortifications were no longer state-of-the-art. Warfare was about to become far more mobile that the World War I commanders could have dreamt.