"The Immigration and Nationality Act of 1952, also known as the McCarran-Walter Act, retained the national origin criterion of 1924. It set an overall ceiling for immigrants and within that ceiling gave each country a cap equal to 1 percent of the individuals of that national origin living in the United States in 1920. The new immigration law, enacted at the height of the Cold War, placed new ideological restrictions on immigration, denying admission to foreign communists. The McCarran- Walter Act also added a series of preferences to the national origins system. The preference system became the basis of a major shift in American immigration policy in 1965. The Hart-Celler Act, also known as the Immigration and Nationality Act of 1965, revised the McCarran-Walter Act and turned U.S. immigration policy in a new direction. Acting in the spirit of recent civil rights legislation, Congress removed the national origins quota system and instead emphasized the preference system. Family reunification became the primary basis for admission to the United States, followed by preferences for people with valuable skills. The Immigration and Nationality Act of 1965 went into effect in 1968, and its liberal provisions made possible another great wave of immigration at the end of the twentieth century. Along with those classified as immigrants, the United States also received large numbers of refugees, leading to the passage of the Refugee Act of 1980 to accommodate this additional group of arrivals. By the end of the twentieth century, new concerns over immigration, especially growing undocumented immigration, led the nation to attempt to control the flow across the borders."