Documented, "legal" immigration is a relatively new phenomenon in the United States—neither the prehistoric settlers who crossed the Ice Bridge nor 16th-century European colonists from the Old World were especially concerned with presenting their papers—but in a contemporary nation with a nationalist streak and a finite job market, it can be serious business.
Note: This timeline focuses on undocumented immigration from Mexico and Latin America, because that's the current focus of the civil liberties debate over immigration, but as many as 1 in 5 immigrants may hail from other parts of the world, most notably Asia.
The Mexican-American border took shape with the Treaty of Guadalupe, which ended the Mexican-American War. About 45 percent of the land previously known as Mexico was ceded to U.S. authorities, who were happy to claim it under the doctrine of Manifest Destiny.
The first large-scale use of undocumented Mexican-American labor came about during the 1880s as industrialists began to construct a railroad to connect Mexico and the United States. The first train crossed the border on August 2nd, 1882, but thousands of undocumented railroad workers crossed the border first.
The Mexican Revolution sent tens of thousands of Mexican migrant workers to the United States, as the economy south of the border changed and the economy north of the border entered a more progressive, worker-centered era.
As the declining U.S. economy led non-Latino workers to fight for jobs, the first round of Mexican deportations forcibly sent millions of "illegal" immigrants—including between 500,000 and two million U.S. citizens of Latino ancestry—to Mexico.
Mass deportation opened up job opportunities for desperate non-Mexican workers during the Great Depression, but World War II created millions of vacancies, particularly in the agricultural industry. The U.S. government's Bracero Program attempted to resolve some of these issues by importing Mexican migrant workers to perform many of the duties previously performed by men serving overseas. The program worked out so well that the government continued to operate it until 1964.
The racist term "wetback" came into common parlance after the implementation of Operation Wetback, a 1954 program to deport undocumented Mexican-American workers who did not fall within the Bracero Program's mandate (which included quotas, as well as strict labor and pay standards). Over one million undocumented workers were deported to Mexico.
Consistent with the goals of the civil rights movement, the Immigration Act of 1965 revised the entire U.S. immigration system by removing quotas based on race and implementing more general quotas.
By 1986, some three million undocumented immigrants had come to reside in the United States. President Ronald Reagan, Senator Ted Kennedy (D-MA), and the congressional leadership worked together to grant amnesty to these immigrants in a bill that simultaneously introduced stricter penalties for employers who hire undocumented immigrants. The penalties were never substantially enforced, so the primary mechanism of enforcing immigration policy in subsequent years consisted of sporadic raids and deportations.
The passage of the North American Free Trade Agreement (NAFTA), coupled with the Mexican economic collapse of 1994, brought an estimated 13 million new undocumented immigrants to the United States over the next 15 years.
The passage of Arizona SB 1070, which allows law enforcement officials who have not been trained in immigration policy to demand papers from any Arizona residents they deem suspicious, is generally regarded as one of the most blatant examples of racial profiling legislation in U.S. history. Even as its status is currently being assessed by the federal court system, other states are considering similar legislation.