SAN SALVADOR — In the 1980s, the United States gave the tiny country of El Salvador billions in military and economic aid in an effort to to undermine a leftist insurgency. Washington’s argument for doing so was that El Salvador was a crucial laboratory to determining the future of Latin America.

El Salvador has indeed gone on to profoundly shape Latin America, just not in the ways envisioned by the cold warriors. In the end the insurgents of the Farabundo Martí National Liberation Front, or F.M.L.N., never did succeed in establishing the Soviet proxy state that the Carter and Reagan administrations feared. But the brutal civil war set in motion cycles of violence and impunity that have unleashed waves of migration to the United States.

I returned here last month as part of a delegation examining the root causes of Central American migration to the United States. We toured the Catholic university campus where 30 years ago six Jesuit priests, their housekeeper and her teenage daughter were killed by a Salvadoran military unit trained by the United States.

The Rev. José María Tojeira, who was then the head of the Jesuit order for Central America, was among the first to see the bodies. At the time he recounted to reporters how “they were assassinated with lavish barbarity.” “ They took out their brains,” he said.