Why has the population of the South and the West increased so dramatic

Why has the population of the South and the West increased so dramatically in the late twentieth century? Why didn’t significant numbers of people move to these sections before World War II?

What will be an ideal response?

ANSWER
Air conditioning helped cause industries to relocate in the South and retirees to move south for the weather and lower cost of living. Improved race relations also made the South more attractive. Industries moved south and west (and created jobs) because of lower wages, weaker unions, lower taxes, fewer regulations, and more state and local subsidies and incentives. The West became more attractive due to jobs created by wartime and Cold War defense industries and military bases, and because of the emergence of the electronic, aerospace, and other high technology industries.