http://en.wikipedia.org/wiki/History_of ... of_America

In 1954, Operation Wetback forced the return of thousands of illegal aliens to Mexico. Between 1944 and 1954, "the decade of the wetback," the number of illegal immigrants coming from Mexico increased by 6,000 percent. It is estimated that, in 1954, before Operation Wetback got under way, more than a million workers had crossed the Rio Grande illegally. Cheap labor displaced native agricultural workers, and increased violation of labor laws and discrimination encouraged criminality, disease, and illiteracy. According to a study conducted in 1950 by the President's Commission on Migratory Labor in Texas, the Rio Grande valley cotton growers were paying approximately half of the wages paid elsewhere in Texas. The United States Border Patrol aided by municipal, county, state, and federal authorities, as well as the military, began a quasi-military operation of search and seizure of all illegal immigrants. Fanning out from the lower Rio Grande valley, Operation Wetback moved northward. Illegal immigrants were repatriated initially through Presidio because the Mexican city across the border, Ojinaga, had rail connections to the interior of Mexico by which workers could be quickly moved on to Durango. The forces used by the government were actually relatively small, perhaps no more than 700 men, but were exaggerated by border patrol officials who hoped to scare illegal workers into flight back to Mexico. Ships were a preferred mode of transport because they carried the illegal workers farther away from the border than did buses, trucks, or trains. It is difficult to estimate the number of illegal immigrants that left due to the operation--most voluntarily. The INS claimed as many as 1,300,000, though the number officially apprehended did not come anywhere near this total.