region comprising 15 southern states in the United States and extending from Virginia and Florida in the southeast through Nevada in the southwest, and also including southern California. Between 1970 and 1990, the South grew in population by 36 percent and the West by 51 percent, both well above the national average. Large in-migration, along with a high birth rate and a decline in out-migration, all contributed to rapid growth of both the Sun Belt's population and manufacturing activities. Improvements in transportation and communications, abundant air conditioning in summer, and a favourable winter climate are attractive forces for retirees as well as workers.