Since the mid-1800's, migrations have been common in America. The first great migration that changed the country was of foreign immigrants seeking a better life—the Irish, Italians, Eastern Europeans and other religious and ethnic groups that usually ended up in the big cities of the East or the farms of the Midwest. During the Industrial Revolution and thereafter, millions of Americans migrated to the cities to look for factory work, and, in the case of African Americans, escape the rural South into the urban North. But nothing compared to the massive migration of the Second World War.
Some of that migration was involuntary. Fifteen million men and several hundred thousand women - one in nine Americans - left home for military training camps. 3/4 of those ended up overseas, six times the number that had gone to France in World War One. Back home, another fifteen million people were on the move, usually looking for work. And with wartime industrialization at a fever pitch, work was everywhere. Labor shortages drove workers from factory to factory, region to region, seeking better jobs at higher wages. This labor force mobility was such a threat to production schedules that Congress passed the West Coast Manpower Plan, which allowed military production contracts to be granted only where the labor force was already available.
Wartime migration had two major routes: from the South to the North, and even more frequently, from the East to the West. The farmlands of the South and Midwest actually lost population between 1940 and 1945, while the populations of Washington, Oregon and California rose by more than a third. (California alone had 75% more people in 1950 than in 1940. The WW2 home front song could have been "How Ya Gonna Keep 'Em Down on the Farm, After They've Seen Pasadena?") By war's end, one in every five Americans had moved somewhere—eight million to other states.
And it was worth it. Home front Americans had money, and places to spend it. They went to movies and restaurants, and bought books, jewelry, liquor and records as they never had before. Farmers built real homes, with indoor plumbing and running water. Three years to the day after the attack on Pearl Harbor, Macy's Department Store chain had its best day ever at the till.