… A decade ago, the Columbia University historian Mae Ngai published her now-classic book, Impossible Subjects: Illegal Aliens and the Making of Modern America (2004), an authoritative history of the 1965 Act, the immigration laws that preceded it, the political world that made it possible, its most important provisions, and its unforeseen consequences. Many historians and observers have considered the 1965 Act to be a liberal law because it repealed the national-origins quotas codified by the 1924 Johnson-Reed Act, legislation that raised the bar for Southern and Eastern Europeans in particular, who, at the time, were seen as socialists or anarchists. The exclusion of other groups, such as Filipinos, Chinese, Japanese, and Indians—Asians, in other words—had been repealed before the sixties, but the 1965 Act would close the books, once and for all, on the long era of nation-based exclusion.

The liberal framers of the 1965 Act sought reform primarily to achieve formal equality for immigrants from all nations. Especially in the context of post–World War II pluralism, demands during the Cold War for racial equality, and burgeoning civil rights struggles, the 1965 Act symbolized America's democratic traditions in practice. Liberals and conservatives generally agreed on the law's preference for highly skilled immigrants, but they did not see eye to eye on questions of how many immigrants in total would be permitted and whether or not the law would place restrictions on immigrants from the Western Hemisphere. Liberals argued for a greater number of immigrants than conservatives wanted (500,000 or more compared with 250,000 or fewer) and, in keeping with earlier practice, pushed for no restrictions on Western Hemisphere countries. But LBJ and other Democrats argued that compromise was necessary. In the end they agreed to the modest figure of 290,000 total immigrants per year—or 170,000 from the Eastern Hemisphere and 120,000 from the Western Hemisphere—and a numerical cap of 20,000 on immigrants from any single country.

Despite the rhetoric of equal treatment under the law, the 1965 Act bred inequality and was, at its core, restrictive and "conservative." This was perhaps Ngai's most important insight: the law led to inclusion, but it led to even greater exclusion. For the first time in history, the 1965 Act placed a numerical restriction on immigrants from Western Hemisphere countries such as Mexico. No prior immigration law restricted the immigration of Mexicans or other Latin Americans, in part because business owners relied on their labor. Instead, their immigration was regulated according to the demands of the U.S. labor market. So when the 1965 Act set the number of Mexicans who could immigrate legally at 20,000 per year despite the demands of employers for a much greater number, it guaranteed a spike in undocumented immigration, a subject that had garnered national attention before, especially during the anti-"wetback" hysteria of the mid-1950s, but never with the vitriol that characterized it from the late 1960s onward. (2)

At the same time, the Mexican economy could not absorb all of the workers who returned home at the conclusion of the guest-worker initiative known as the Bracero Program. Between 1942 and 1964, the Bracero Program facilitated the migration of some 4.5 million Mexicans to the United States. Other mechanisms made legal migration possible as well, such as crossing cards that enabled Mexicans living near the border to work in the United States, but not nearly on the scale of the Bracero Program. Originally designed as an emergency wartime measure that would replace enlisted Americans, the program endured well into the postwar era because U.S. employers needed low-wage labor. Their need, of course, lasted beyond 1964, too, but the U.S. and Mexican governments ended the program primarily due to pressure from labor and civil rights organizations, which argued that braceros competed with American workers and that the program exploited the Mexican laborers. Since little work was available to them back home in Mexico, when the program ended many former braceros again headed north to the United States, this time illegally. Such unforeseen consequences of the 1965 Act helped imprint our national conscience with the image of Mexican immigrants as the archetypal "illegal aliens.”...