A number of major laws and court decisions relating to immigration procedures and enforcement have been enacted for the United States.
Naturalization Act (officially An Act to Establish a Uniform Rule of Naturalization; ch. 54, 1 Stat. 566)
Alien Friends Act (officially An Act Concerning Aliens; ch. 58, 1 Stat. 570)
Alien Enemies Act (officially An Act Respecting Alien Enemies; ch. 66, 1 Stat. 577)
Several years later, in the wake of the 1906 San Francisco Earthquake and Fire, a number of Chinese immigrants who were otherwise subject to the Chinese Exclusion Act were nonetheless able to claim American citizenship by alleging they were born in San Francisco, and that their birth certificates had been destroyed along with those of everyone else who had been born in San Francisco. "Papers for fictitious children were sold in China, allowing Chinese to immigrate despite the laws."
"An unintended consequence of the 1920s legislation was an increase in illegal immigration. Many Europeans who did not fall under the quotas migrated to Canada or Mexico, which [as Western Hemisphere nations] were not subject to national-origin quotas; [and] subsequently they slipped into the United States illegally."
Federal officials deported "Tens of thousands, and possibly more than 400,000, Mexicans and Mexican-Americans... Many, mostly children, were U.S. citizens." "Applications for legal admission into the United States increased following World War II — and so did illegal immigration." Some used fraudulent marriages as their method of illegal entry in the U.S. "Japanese immigration became disproportionately female, as more women left Japan as "picture brides", betrothed to emigrant men into the U.S. whom they had never met."
The United States saw a total number of illegal immigrants estimated at 1.1 million, or half of one percent of the United States population.
Over 5.8 million illegal immigrants entered the US in the 1990s. Mexico rose to the head of the list of sending countries, followed by the Philippines, Vietnam, the Dominican Republic, and China.