series of acts that regulated the flow of immigrants into the United States. Beginning in the 19th century, Congress enacted a series of restrictive immigration laws that sought to limit or bar those immigrants who were thought to be undesirable (e.g., Chinese and Japanese persons, the illiterate, the sick or handicapped, criminals, political radicals). In the early part of the 20th century a commission set up to study the issue recommended a quota system, which was adopted in the Immigration Act of 1924, formerly 8 U.S.C. § 145 et seq. This act established an annual quota, fixed in 1929 at 150,000. It also established the national-origin system, under which quotas were established for each country based on the number of persons of that national origin who were living in the United States in 1920. It thus discriminated in favor of the countries of northwestern Europe and against immigrants from southern and eastern Europe; it barred Asians completely. Although minor changes were subsequently made, this law was to characterize national immigration policy until 1965, when it was abolished in favor of a first-come, first-serve policy. The new law set an annual ceiling of 170,000 immigrant visas for nations outside the Western Hemisphere, with 20,000 the maximum allowed to any one nation. A ceiling of 120,000 was set for persons from the Western Hemisphere. A law in 1986 granted amnesty to many illegal aliens already in the United States and imposed sanctions on employers who knowingly hire illegal aliens. Additional revisions were made in 1990, including increasing limits on immigration. Laws passed in 1996 and 2005 sought to strengthen the enforcement of immigration laws.