Tweet   Wehrmacht 1940 invasion of France.  The Maginot Line was a series of defensive fortifications, tank obstacles, artillery casemates, machine gun posts, and other defences built by the French after WWI to guard against invasion by Germany or Italy. It is considered by many to be one of the great military mistakes of all time, since the Maginot Line ultimately made little difference in WWII, and More..was fairly easily bypassed by the Germans, who conquered France by 1942.