These families included 2,206 adults and 2,342 children, according to statistics released by the Department of Homeland Security. Nearly all of these migrants came from El Salvador, Honduras and Guatemala, seeking asylum from a surge of gang violence and instability in those countries in recent years.

Under the Obama-era policy, families who tried to cross the border illegally could be detained for months but were kept together. The government hoped the indefinite detainment would deter future migrants, but in 2015 a federal judge ruled it was illegal to hold children for that long. Rather than separate the families, the government chose to release them.

Between April 19 and May 5, the Trump administration rolled out a "Zero Tolerance" policy, charging every adult who crossed the border illegally with criminal entry into the U.S. Because children are not allowed in federal prisons, families were separated upon the parents' arrest.

The children were held in DHS processing centers, like this one in McAllen, Texas, for up to 72 hours before they were referred to the Department of Health and Human Services' Office of Refugee Resettlement.

If the ORR could not find relatives in the U.S., children were sent to a shelter or foster family, joining the more than 11,800 minors in ORR's care. In response to the rising number of children held without parents, the government also prepared to move some to military bases and temporary facilities like this tent camp in Tornillo, Texas.

Meanwhile, the adults were brought before a judge to face a misdemeanor charge of illegal entry. Upon pleading guilty, they were usually sentenced to time served or a few days in jail, and then placed in Immigration and Customs Enforcement custody to await deportation or an asylum hearing. Some parents said they were deported without their child.

In response to public outcry, President Donald Trump signed an executive order on June 20 that allows the DHS to detain families together. While details are still unclear, some officials also say they are no longer prosecuting every adult. However, it is still unclear how children now in custody will be reunited with their parents.