The specific process is that after World War I, the French government has been trying to restrict Germany through the Versailles system to prevent it from making a comeback, and even directly sent troops to occupy Ruhr-gebiet, Germany; After Hitler came to power, he tore up the Treaty of Versailles and expanded his army to prepare for war. During World War II, France was occupied by Germany. After Germany declared war on Poland, in order to fulfill its commitment to Poland, Britain and France declared war on Germany on September 3, 1939.
Later, the Germans bypassed maginot line, France was defeated, and Petain established Vichy France. It was not until Charles de Gaulle's free France and allied forces defeated Germany that the war between France and Germany came to an end. 1944- 1945 with the allied occupation of western Europe, Germany was defeated and France recovered.