Families arrive at a bus station after being released from Customs and Border Protection in McAllen, Tex. (Spencer Platt/Getty Images)
Paul A. Kramer is an associate professor of history at Vanderbilt University and the author of "The Blood of Government: Race, Empire, the United States and the Philippines."

The Trump administration’s recent policy of separating families and imprisoning children who cross the U.S. border with Mexico — some version of which may resume after a 20-day hiatus — is only the latest episode in a larger, ongoing assault on migrant families. The assault includes ICE raids, family detentions, mass deportations, the Muslim immigration ban and the condemnation of family-assisted immigration (“chain migration”) as a threat to the nation.

Together, they represent a wholesale attack on a long-standing cornerstone of U.S. immigration policy: the pursuit of family unity.

It took decades of activism by immigrants and advocates to achieve family-based admissions. And both family-unification policies and the motives behind them were flawed. But it’s striking how consistently U.S. immigration law — including some of the country’s most racist and restrictive immigration policies — has prioritized keeping some kinds of families together. Everyone from liberal proponents of immigration reform to reactionaries looking to whiten America have found something to like in family unification, which helps explain the widespread outrage as Americans saw images of families wrenched apart.

The Emergency Quota Act of 1921 and Immigration Act of 1924, for example, both used discriminatory quotas to restrict migration from southern and Eastern Europe. Yet both also came with family-based clauses. The former gave quota preferences to the “wives, parents, brothers, sisters, children under 18 years of age, and fiancees” of naturalized immigrants and legal residents who had applied for U.S. citizenship. The latter allowed the wives and minor children of naturalized immigrants to enter outside the quotas, while providing quota preferences for them, as well as parents.

There were stark limits to these policies. Most of the world’s families did not conform to the constricted definitions contained in U.S. immigration law. Establishing the legitimacy of one’s family with U.S. immigration officials was laborious and risky, and many family petitions were rejected, which promoted unauthorized migration.

The emphasis on family unity cuts both ways: Restrictionists invoked it to argue that immigrant men who arrived without families should be denied citizenship because they had abandoned their loved ones. And the flip side of these family preferences was the stigmatizing of immigrants traveling outside “normal” families, particularly women unaccompanied by men, who were presumed to be sex workers.

Policies that preserved family links also frequently came with troubling rationales. Some argued that heterosexual marriage could make “undesirable” immigrants more moral and productive, as well as less likely to claim public resources. Others thought male immigrants should not be denied their manly rights to their wives’ labor and companionship.

Even as some laws made it easier for some families to remain together, other laws divided them. The “guest worker” programs of the mid-20th century, for example, which brought in millions of Mexican and Caribbean men to labor in the fields, officially prohibited them from bringing their families, so that employers could minimize their pay and the state could pressure them to return to their home countries.

But claims about the importance of family unity ultimately proved a potent resource that immigrant communities and their advocates used in their efforts to shatter the United States’ restrictionist immigration laws. Through intense lobbying and campaigning, immigrants, especially as second-generation communities grew (and organized and voted), worked to make keeping families together the dominant priority in post-World War II immigration reform.

Taking advantage of new legislative precedents, like the postwar “war brides” acts, which admitted the foreign-born wives of U.S. servicemen, reformers gained traction in an era that enshrined specific kinds of families as embodiments of an American ideal of consumption, suburbia and the good life. Speaking in 1956, President Dwight D. Eisenhower noted that there was “increasing apprehension among our citizens … about the moral principle involved when we keep children and spouses apart from fathers and husbands for many years by immigration barriers.”

During the 1960 presidential race, Richard Nixon and John F. Kennedy each spoke of the importance of family reunification. Nixon stated that the United States had “been built by immigrants from other countries” and that “[humanitarianism] itself calls for action to bring about a reunion of immediate family members under preferential quotas.” Kennedy agreed, arguing that Americans had “a social obligation” to reunite families and that it should be immigration reform’s most immediate objective.

New Cold War arguments about family unity also bolstered the cause. Helping families to reunite would attract skilled, talented people who would help the United States beat the Communists while sending the right messages out into the world about the United States as a humanitarian society.

As new legislation was debated in the early 1960s, family unity figured prominently in arguments for reform. Rep. Michael Feighan (D-Ohio) spoke of “the large numbers of families in our nation, split and separated by war, tyranny and human upsets.” This was “difficult if not impossible to justify in light of the primary moral value our society attaches to the integrity of the family.” As he put it: “Families, split and divided by peculiarities of law rather than free choice … are at variance with our longstanding tradition.”

But again, the conception of family was narrow, restricting immigration opportunities to heterosexual families, for example. It wouldn’t be until 2013 and the Supreme Court’s decision in United States v. Windsor that same-sex couples would be granted equal status when it comes to immigration.

Advanced by liberal reformers in the 1960s, family reunification also made strange bedfellows. Racist policymakers did not anticipate non-European mass migration and thought the policy would attract white European immigrants who posed no threat to their vision of white supremacy. Segregationist Sen. Strom Thurmond (R-S.C.) said, “Blood relationships and family ties stem from the same sense of identity and preference,” and thus it is “most desirable that unification of families be a major consideration in our immigration formula.”

Thus, for good and bad reasons, family unification became the basis of the 1965 immigration reform legislation, the Hart-Celler Act, that replaced the old quota system. It was right there in the law’s distribution of visas: a full 74 percent were allotted to family reunification cases.

Despite expectations, reform didn’t draw in more Europeans. Instead the new system brought communities of Asian, Latin American and African migrants to the United States, building a newly diverse and culturally vibrant country. In practical terms, this policy has also helped to alleviate hardship and enable many migrants to navigate the forces of a globalizing world, which often split and scatter families. For better and worse, it has contributed to Americans’ sense that their country’s immigration policies are rooted in humanity and decency: that the unfolding brutalities along the border are “not who we are.”

It is in part out of this optimistic (and somewhat self-deceiving) sense that President Trump’s policies have triggered such opposition. But as our horror widens, our demand that 4-year-olds not be ripped from their parents must be understood as a minimalist one, one that we should be collectively ashamed to have to insist on.

The terrorizing of migrant families did not begin with the forced removal of children from their parents, and it will not end with its promised passing. We must remain vigilant and press further in protecting the vulnerable from this administration’s ever-deepening depravities. We must stand against the separation of parents from minor children at the U.S.-Mexico border and, as we do so, continue to fight the abuse of families that are not made to suffer separation, and the broader, poisonous division of the human family advanced by these injustices.