Strategy (and tactics) must constantly evolve in response to technological advances. A successful strategy from one era tends to remain in favor long after new developments in military weaponry and matériel have rendered it obsolete. World War I, and to a great extent the American Civil War, saw Napoleonic tactics of "offense at all costs" pitted against the defensive power of the trench, machine gun and barbed wire. As a reaction to her World War I experience, France entered World War II with a purely defensive doctrine, epitomized by the "impregnable" Maginot Line, but only to be completely circumvented by the German blitzkrieg in the Fall of France.