The Chinese Exclusion Act was the first significant law passed that restricted immigration into the United States. It was passed by Congress in 1882 in response to the belief of west coast workers that Chinese immigrants were bringing down wages and causing economic troubles, even though the Chinese comprised only .002 percent of the population.
The law, which suspended Chinese immigration for ten years, was renewed in 1892 for another ten years. In 1902, Chinese immigration was made "permanently" illegal and the Chinese remained ineligible for citizenship until 1943.
The Chinese Exclusion Act was part of a long history of nativism in the United States. Attempts throughout history have involved efforts to restrict and deny citizenship to various ethnic, religious and national groups. In the 1830s, efforts were focused on keeping Catholics from obtaining citizenship, based on a belief that Democracy and Catholicism were incompatible. A popular parlor game enjoyed at the time was called "Break the Pope's Neck."
One of the odd elements of irony in the United States' long history of immigration restriction and attacks on immigrants is found in the Declaration of Independence. There one can read complaints about King George III's restriction of immigration in an effort to depress the population of the United States and keep it an English based colony.
In the late 18th century, the first move against immigration was politically based. Members of Congress who opposed Thomas Jefferson's Republican faction passed the Alien Acts in 1798 in response to their realization that most immigrants tended to support Jefferson.
To this day, immigration remains a complicated process with dozens of laws open to individual interpretation. The process can take months and years. This has most commonly been associated with economic concerns, in the form of fear that immigrants will bring down wages and increase unemployment amongst "native" Americans. Whether or not this is true is a subject of much debate, with some believing the complexities of immigration policy create a culture of illegal immigration and crime and that easier immigration laws would provide a stronger economic base due to the immigrants' need for goods and services.