At home, the U.S. had experienced sustained economic expansion and a rapid growth of its population and middle class following World War II. After a surge in female labor participation, especially in the 1970s, by 1985, the majority of women aged 16 and over were employed. Construction of an Interstate Highway System transformed the nation's infrastructure over the following decades. Millions moved from farms and inner cities to large suburban housing developments. In 1959, the United States formally expanded beyond the contiguous United States when the territories of Alaska and Hawaii became, respectively, the 49th and 50th states admitted into the Union. The growing Civil Rights Movement used nonviolence to confront segregation and discrimination, with Martin Luther King Jr. becoming a prominent leader and figurehead. A combination of court decisions and legislation, culminating in the Civil Rights Act of 1968, sought to end racial discrimination. Meanwhile, a counterculture movement grew, which was fueled by opposition to the Vietnam war, the Black Power movement, and the sexual revolution.