Statutory limits on immigration to the United States in effect from 1968 to October 1978. Mandated by the Immigration and Nationality Act Amendments of 1965, the ceiling on immigration from the Eastern Hemisphere was set at 170,000, with a per-country limit of 20,000. Immigration from the Western Hemisphere was held to 120,000, without a per-country limit until January 1, 1977. The Western Hemisphere was then made subject to a 20,000 per country limit. Effective October 1978, the separate hemisphere limits were abolished in favor of a worldwide limit.
Source: U.S. Citizenship and Immigration Services