(2) Petro- chemical Explanation: The Sun Belt is a region of the United States which became synonymous with the southern third of the nation in the early 1970s when there was a shift in this period from the previously economically and politically important northeast to the south and west. Industries such as aerospace, defence, and oil boomed in the Sun Belt as companies took advantage of the low involvement of labour unions in the south (due to more recent industrialization; 1930s through 1950s) and enjoyed the proximity to many U.S. military installations who were the major consumers of their products. The oil industry helped propel southern states such as Texas and Louisiana forward.