It was a civil war of the 1980s, one that pitted leftist revolutionaries against the alliance of countries, oligarchs, and generals that had ruled the country for decades—with U.S. support—keeping peasants illiterate and impoverished. It was a bloody, brutal, and dirty war. More than 75,000 Salvadorans were killed in the fighting, most of them victims of the military and its death squads. Peasants were shot en masse, often while trying to flee. Student and union leaders had their thumbs tied behind their backs before being shot in the head, their bodies left on roadsides as a warning to others.

President Trump might wonder what Ronald Reagan—one of his favorite presidents—was doing pouring billions of dollars of economic and military aid into the tiny country. In the early ‘80s, El Salvador was receiving more such aid than any country except for Egypt and Israel, and the embassy staff was nearly as large as that in New Delhi. For Reagan, El Salvador was the place to draw the line in the sand against communism.

Many Americans would prefer to forget that chapter in American history; those under the age of 40 may not even be aware of it. Salvadorans haven’t forgotten, however. In El Mozote and the surrounding villages of subsistence peasants, forensic experts are still digging up bodies—of women, children, and old men who were murdered by the Salvadoran army during an operation in December 1981. It was one of the worst massacres in Latin American history. But while Trump might smear the country’s image with crude language, today El Salvador has a functioning legal system—more than three decades after the event, 18 former military commanders, including a former minister of defense, are finally on trial for the El Mozote massacre.

Some 1,200 men, women and children were killed during the operation. Old men were tortured. Then executed. Mothers were separated from their children. Raped. Executed. Crying, frightened children were forced into the convent. Soldiers fired through the windows. More than a hundred children died; their average age was six.

“The United States was complicit,” Todd Greentree, who was a young political officer at the American embassy at the time, told me recently in an interview for a documentary about the massacre. Greentree noted that the massacre was carried out by the Atlacatl Battalion, which had just completed a three-month counterinsurgency training course in the United States. That training was also supposed to instill respect for human rights. The El Mozote operation was the battalion’s very first after completing the course.

When reports of the massacre first appeared in The New York Times and The Washington Post, the American ambassador, Deane Hinton, sent Greentree and a military attaché, Marine Corps Major John McKay, to investigate. They concluded there had been a massacre, and that the Atlacatl battalion was responsible, Greentree told me.