The Cook County suburbs grew rapidly after 1945, but the Democratic party machine kept both the city and suburbs under control, especially under mayor Richard J. Daley, who was chairman of the Cook County Democratic Party. Deindustrialization after 1970 closed the stockyards and most of the steel mills and factories, but the city retained its role as a financial and transportation hub. Increasingly it emphasized its service roles in medicine, higher education, and tourism.