That’s because, by the mid-1960s, the American appetite for the cheapest possible immigrant labor had become insatiable. At the same time, Mexico’s population was growing exponentially, with a labor market that failed to provide sufficient economic opportunities for working-age people. Despite this potential parity between supply and demand, Mexicans only rarely received the necessary visas for legal immigration to the United States, because in spite of its liberalism in other areas, the 1965 Immigration and Nationality Act placed an annual cap of 120,000 migrants from the entire Western hemisphere. Together, all these factors helped the number of undocumented immigrants from Mexico to skyrocket after 1970.
By the 1970s, the U.S. economy itself had begun to change significantly. The manufacturing industry was in decline. Native-born citizens were moving away from small family farms, while farmland was consolidated into larger operations that depended on immigrant labor. And the service sector — which includes restaurants, hotels, cleaning and maintenance, among other things — was also growing rapidly.