Rescuers prepare to lower a U.S. Marine onto a stretcher following an explosion at the Marine Command Base in Beirut, Lebanon, Oct. 23, 1983.

When an international peacekeeping force arrived in war-torn Lebanon in 1982, it included a contingent of 800 U.S. Marines contributed by President Ronald Reagan. But the force's mission of preserving the shaky Lebanese government turned into a bloody debacle for America. On October 23, 1983, a suicide bomber drove a truck loaded with explosives into the Marines' compound, killing 241 Americans and wounding another 100.

Within six months, the U.S. peacekeepers withdrew. But radical Islamists and anti-American terrorist organizations got the message that Americans no longer had much stomach for suffering casualties in interventions — a realization that would inspire additional attacks on U.S. forces in Somalia, Saudi Arabia and Yemen in the years to come.

The same month as the Lebanon disaster, on the Caribbean island of Grenada, the military overthrew and assassinated leftist Prime Minister Maurice Bishop (who himself had seized power in a less bloody coup several years earlier). President Reagan, saying that he needed to protect American students at a Grenadan medical school and prevent the country from becoming a Soviet base in the Carribean, sent the U.S. military to overthrow the rebels.

But sometimes the Reagan Administration preferred to use less direct methods of intervention. In the president's quest to prevent the spread of communism, he developed the Reagan Doctrine. In some Third World countries, the United States would expand military and economic aid to governments battling leftist rebels. Elsewhere, conversely, the United States would help rebel movements try to overthrow leftist regimes. In El Salvador, the United States spent $4 billion assisting the government in a civil war against the leftist Farabundo Martí National Liberation Front. Despite the U.S. involvement, the civil war lasted until 1992 and claimed tens of thousands of mostly civilian lives.

In Nicaragua, President Reagan spent millions backing the Contras, a rebel movement that included former supporters of dictator Anastasio Somoza Debayle. The U.S.-backed rebels failed to militarily overthrow the leftist Sandinista regime, but their raids wreaked economic havoc. That damage, combined with a U.S. trade embargo, an American effort to block international loans to Nicaragua and the leftist government's own mismanagement and corruption, forced the financially strapped Sandinistas to cut back on social services. In 1990, they lost an election to a U.S.-supported opposition party headed by Violeta Barrios de Chamorro.