The Vietnam conflict continues to be the touchstone for both the military and policy makers committed to avoiding future foreign military "quagmires." As the United States made the seemingly inexorable transition from being advisors to undertaking covert operations, bombing and deploying ground troops, the strategy of "incremental escalation" emerged as the military's bête noire. Military frustrations during the "war without fronts" were heightened by diplomatic and humanitarian constraints on operations in North Vietnam. Protest and resistance at home and abroad underlined the pitfalls of pursuing prolonged, costly and divisive wars alone. And the ultimate defeat of South Vietnam in 1975 strengthened the resolve of those who would avoid "unwinnable" limited wars in the future.

Sandstorms and equipment malfunctions caused the cancellation of the surprise attempt to rescue over sixty American hostages held by revolutionary students at the U.S. embassy in Tehran. Failure turned deadly when eight Americans were killed after a helicopter and a transport plane collided at a remote desert staging area. The disaster reflected military disarray and lack of preparedness and, after Ronald Reagan took office, helped launch the largest peacetime defense build-up in the nation's history.

Twice during the early 1980s the United States deployed troops to Lebanon to deal with the fall-out from the Israeli invasion. In the first deployment, U.S. marines helped oversee the withdrawal of the PLO from Beirut. In the second deployment, 1,800 marines were sent as part of a multinational force after Israel's Lebanese allies massacred civilians in the Palestinian refugee camps. Given a vague mandate to restore order, support the weak Lebanese government, and work for the withdrawal of all foreign forces, the troops slowly became entangled in the Lebanese civil war. On October 23, 1983, a truck bomb exploded at the vulnerable marine headquarters, killing 241 marines -- the largest loss of life in a military operation since Vietnam. For the military, Beirut becomes a symbol of ill-considered political objectives and poorly-defined rules of engagement.

Within days of the Beirut disaster, President Reagan ordered the invasion of Grenada, following the overthrow of Marxist President Maurice Bishop. Planners sought to protect 600 American students on the Caribbean island, and head off the possibility of another hostage scenario only two years after the freeing of the Iran hostages. In addition, the Reagan administration sought to use the invasion to eliminate Cuban and Soviet influence in Grenada. U.S. forces faced greater than expected resistance and took significant casualties. Though later cited as a model for similar actions, the operation also pointed up serious problems, including inadequate intelligence, poor communications, and inter-service rivalries.

Following a bomb attack on a West Berlin discotheque frequented by American servicemen, the Reagan administration launched a punitive raid on Libya, the suspected sponsor of the bombing. Planes from aircraft carriers and Britain targeted sites allegedly associated with the training and support of terrorist activities. The raid was also part of a larger struggle with Libya throughout the 1980s over its support for international terrorism and its claims over the Gulf of Sidra. Though its long-term utility was debated, the attack was evidence of the Reagan administration's increasing willingness to use military force in pursuit of certain discrete, limited goals -- despite the Weinberger doctrine.

Involving over 27,000 U.S. troops, the Panama invasion was, up to that time, the largest American military operation since the Vietnam War. Dubbed "Operation Just Cause," the intervention's stated goals were the protection of the Panama Canal and the lives of 35,000 Americans in Panama, as well as the promotion of democracy and an end to drug trafficking. The powerful surprise attack quickly overwhelmed the Panamanian defense forces and resulted in the capture of its leader, Manuel Noriega.

To force Iraq out of Kuwait, George Bush formed a large and diverse international coalition and deployed over a half-million U.S. personnel to the Persian Gulf region as part of an allied force. The success of Operation Desert Storm set a new high-water mark for the military and underscored the principle of committing overwhelming force to clear and achievable objectives. Both allied and popular support was largely maintained throughout the campaign. In this way, the Gulf War appears to validate the military doctrine espoused by Joint Chiefs of Staff Chairman Colin Powell.

More on the Persian Gulf War.

Toward the end of the Bush administration, the United States sent approximately 25,000 troops to Somalia to assist the United Nations with the distribution of famine relief supplies. By the time Bill Clinton took office in 1993, U.S. troop levels had been vastly reduced, largely replaced with forces operating under the UN flag. However as UN clashes with local "warlords" increased, American troops became engaged in policing and wider peacekeeping operations. After 18 U.S. Rangers were killed in a firefight in Mogadishu on October 3, 1993, the United States briefly reinforced its troops but retreated from the more ambitious "nation-building" agenda previously outlined by Secretary of Defense Les Aspin. Criticized for having made decisions that may have contributed to the disaster, Aspin resigned two months later.

More on the firefight in Mogadishu.

After negotiations and sanctions failed, Clinton sent U.S. troops to Haiti to restore ousted President Jean-Bertrand Aristide to power and to head off a potential wave of Haitian refugees. A last-minute deal, brokered by former President Jimmy Carter, allowed the troops to go ashore unopposed by the Haitian military and police. Most U.S. troops withdrew within a year, though several hundred remained to pursue a wide agenda of peacekeeping, humanitarian and engineering activities. While Clinton administration officials consistently hailed the intervention as a model effort to restore democracy and promote stability abroad, political, economic and social conditions gradually eroded. In March 1999, the U.S. commander responsible for the remaining military personnel reportedly recommended ending the five-year military presence on the island due to continuing instability.

Following the deadly bombing of a Sarajevo marketplace, NATO forces launched the largest military action in the alliance's history. Two weeks of NATO air strikes, combined with a strong Croat-Muslim offensive on the ground, pushed Bosnian Serbs to the negotiating table. In November, all the warring parties met in Dayton, Ohio and agreed to a peace settlement. The airstrikes, painstakingly approved after years of negotiations with allies and the military, appear to support the position that limited military attacks can be useful diplomatic tools.

Citing Serb atrocities and ethnic cleansing in Kosovo, the U.S. and NATO unleashed air attacks on Serbia after the failure of the "mini-Dayton" peace talks held in Rambouillet, France. President Clinton outlines no "exit strategies" and warns that air strikes will continue as long as necessary. From the start, the Clinton administration ruled out sending U.S. ground troops to the Balkans, though debate over the utility of air power alone repeatedly revives the issue. Vast floods of refugees spill into neighboring countries, threatening to enlarge the crisis and sparking criticism of the lack of contingency planning by NATO.

Sources: Congressional Research Service, "Case studies on use of force by US, 1950-91" Report 92-757-F (1992) 106 pp.; Richard N. Haass, Intervention: The use of American military force in the post-Cold War World (Washington: The Carnegie Endowment, 1994) 259 pp.