Emergency Quota Act of 1921 was considered to be an important legislation from the early twentieth century. This legislation utilized immigration statistics to determine a maximum number of immigrants allowed to enter US borders from each nation or region.
Unfortunately, the numbers were skewed to favor immigration from western European nations while severely curbing immigration from areas perceived to be undesirable. These immigration quotas would change over the years, but would put a lid on fair immigration policy.
The Immigration and Nationality Act, or INA, was created in 1952. Before the INA, a variety of statutes governed immigration law but were not organized in one location. The McCarran-Walter bill of 1952, Public Law No. 82-414, collected and codified many existing provisions and reorganized the structure of immigration law. The Act has been amended many times over the years, but is still the basic body of immigration law.
The Immigration and Naturalization Act of 1965, also known as the Hart-Celler Act, abolished an earlier quota system based on national origin and established a new immigration policy based on reuniting immigrant families and attracting skilled labor to the United States. Over the next four decades, the policies put into effect in 1965 would greatly change the demographic makeup of the American population, as immigrants entering the United States under the new legislation came increasingly from countries in Asia, Africa and Latin America, as opposed to Europe.
http://www.uscis.gov/news/uscis-announces-addition-16-countries-eligibl…
Facts about illegal immigration in the U.S. http://pewrsr.ch/1LoS9Qr