MAP ACTIVITY Map 27.2 The Rise of the Sun Belt, 1940–1980 The growth of defense industries, a non-unionized labor force, and the spread of air-conditioning all helped spur economic development and population growth in the Southwest and the South. This made the Sun Belt the fastest-growing region of the country between 1940 and 1980. READING THE MAP: Which states experienced population growth of more than 20 percent? Which states experienced the largest population growth? CONNECTIONS: What stimulated the population boom in the Southwest? What role did the Cold War play in this expansion? What developments made the Southwest diverse in the composition of its population?