Business, meanwhile, entered a period marked by consolidation. Firms merged to create huge, diversified conglomerates. International Telephone and Telegraph, for instance, bought Sheraton Hotels, Continental Banking, Hartford Fire Insurance, Avis Rent-a-Car, and other companies. The American work force also changed significantly. During the 1950s, the number of workers providing services grew until it equaled and then surpassed the number who produced goods. And by 1956, a majority of U.S. workers held white-collar rather than blue-collar jobs. At the same time, labor unions won long-term employment contracts and other benefits for their members. Farmers, on the other hand, faced tough times. Gains in productivity led to agricultural overproduction, as farming became a big business. Small family farms found it increasingly difficult to compete, and more and more farmers left the land. As a result, the number of people employed in the farm sector, which in 1947 stood at 7.9 million, began a continuing decline; by 1998, U.S. farms employed only 3.4 million people. Other Americans moved, too. Growing demand for single-family homes and the widespread ownership of cars led many Americans to migrate from central cities to suburbs. Coupled with technological innovations such as the invention of air conditioning, the migration spurred the development of "Sun Belt" cities such as Houston, Atlanta, Miami, and Phoenix in the southern and southwestern 31