Thirty years ago this week, President Ronald Reagan made perhaps the most purposeful and consequential foreign-policy decision of his presidency. Though he never said so explicitly, he ended America's military commitment to a strategic mistake that was peripheral to America's interests. Three-and-a-half months after the bombing of the Marine barracks in Beirut that killed 241 U.S. military personnel -- and after repeatedly pledging not to do so -- Reagan ordered the withdrawal of all U.S. troops from Lebanon. As Gen. Colin Powell later aptly summarized this military misadventure: "Beirut wasn't sensible and it never did serve a purpose. It was goofy from the beginning."

What was particularly remarkable about Reagan's bold decision was its rarity. Presidents often authorize using force or deploying troops to achieve some discrete set of political and military objectives. When they prove incapable of doing so with the initial resources and political support, the mission can be scaled back in its scope, enlarged to achieve additional missions, or, the atypical choice, terminated. The latter option requires having the ability to recognize failure, and political courage to end a U.S. military commitment. In large part, it is a combined lack of strategic awareness and political courage that explains many U.S. military disasters. To understand how Ronald Reagan successfully pulled this off, it is worth reviewing and remembering the strategic mistake that was the U.S. military deployment to Lebanon in the midst of that country's wrenching civil war.

Upon the request of the government of Lebanon, the United Nations authorized the Multinational Force in Lebanon (MNF) in 1982 to help the government regain control over the country. There was strong disagreement within the Reagan administration about potential U.S. involvement, with the Joint Chiefs of Staff unanimously opposed to the deployment, and the National Security Council and State Department deeply enthusiastic. Subsequently, the Joint Chiefs developed a range of options for America's participation in the MNF, including sending up to 63,000 U.S. troops to Lebanon to disarm the militias, and enforce the peace in territory under the control of Syria and Israel. Ultimately, without congressional approval, Reagan authorized the deployment of what was seen as a limited mission of some 1,800 Marines, who joined French, Italian, and later British troops. Reagan claimed: "Their mission is to provide an interposition force at agreed locations," but "in carrying out this mission, the American force will not engage in combat."

After the Palestine Liberation Organization (PLO) pulled out of Beirut in August 1982, MNF troops withdrew to their ships offshore. But the assassination of Lebanese President Bachir Gemayel, massacre of Palestinian refugees -- who were living in camps under Israeli military control -- by militias linked to the Maronite Christian Phalange Party, and the subsequent chaos led almost immediately to international support for a second MNF deployment.

It was during this second MNF deployment that the intention and scope of U.S. forces was never quite clear. Shortly after the U.S. troops returned to Lebanese territory, on Aug. 20, 1982, Reagan contended that they would now "assist the Lebanese Armed Forces in carrying out their responsibility for ensuring the departure of PLO leaders, officers, and combatants in Beirut from Lebanese territory," and "facilitate the restoration of the sovereignty and authority of the Lebanese Government over the Beirut area." He added: "In no case will our troops stay longer than 30 days."

On Oct. 28, Secretary of Defense Caspar Weinberger offered his astonishingly contradictory statement: "What we need is a multinational force until certain conditions have been achieved. Nobody knows when those conditions can be achieved. It is not an open-ended commitment." (Weinberger later wrote in his memoir, "I objected [to the deployment], of course, very strongly, because this MNF would not have any mission that could be defined.") State Department official Lawrence Eagleburger, using Iraq surge-like language, later claimed during a congressional hearing that the Marines' mission was ''to provide the Government of Lebanon a breathing spell to begin to sort out the country's political problems.'' By Sept. 29, 1983, Reagan stated: "Their mission is to provide an interposition force at agreed locations and thereby provide the multinational presence as requested by the Lebanese Government to assist it and the Lebanese Armed Forces."

In October 1983, after five Marines were killed in three separate incidents, National Security Advisor Robert McFarlane convinced the president to authorize the USS New Jersey to launch attacks against the Druze militia and Syrian forces on land. According to Powell, once the naval attack commenced, the Shiites "assumed the American 'referee' had taken sides against them. And since they could not reach the battleship, they found a more vulnerable target: the exposed Marines at the airport." Within one week, Hezbollah-linked militants drove two truck bombs containing a half a kiloton of explosives into the Marine barracks at the Beirut International Airport, killing 220 Marines and 21 other U.S. service members.

In the months that followed, the Reagan administration discussed a range of options including striking back and fully withdrawing the Marines. Reagan never retaliated against Hezbollah or their Iranian and Syrian sponsors responsible for the bombings, a position widely endorsed by senior military officials. As then-Chairman of the Joint Chiefs Gen. John Vessey declared: "It is beneath our dignity to retaliate against the terrorists who blew up the Marine barracks."

The Reagan administration also considered the pluses and minuses of withdrawing from the MNF. On the day after the barracks bombing, however, the president reaffirmed his commitment: "The reason they must stay there until the situation is under control is quite clear. We have vital interests in Lebanon. And our actions in Lebanon are in the cause of world peace." Over a month later, on Dec. 1, Reagan stated that the Marines were in Beirut to "demonstrate the strength of our commitment to peace in the Middle East.... Their presence is making it possible for reason to triumph over the forces of violence, hatred, and intimidation." Nine days later, he told the nation: "Once internal stability is established and withdrawal of all foreign forces is assured, the Marines will leave." Finally, on Feb. 4, 1984, Reagan stated something frequently heard in debates over Afghanistan and other theaters of conflict today -- if the United States withdraws, "we'll be sending one signal to terrorists everywhere: They can gain by waging war against innocent people.... If we're to be secure in our homes and in the world, we must stand together against those who threaten us."

Yet, just three days later, on Feb. 7, Reagan ordered the Marines to "redeploy" to their ships offshore -- which was actually a full withdrawal achieved in three weeks. Although the Marine's mission in Lebanon was not clearly defined and, subsequently, not achieved, Reagan's tacit admission of failure and withdrawal of the Marines from Lebanon limited America's further involvement in foreign-policy disaster -- saving money, lives, and time. Many pundits later claimed wrongly that Reagan was erroneous, because Osama bin Laden contended that the withdrawal was a sign of U.S. weakness; as if America's strategic choices should be held hostage to how terrorists choose to describe them.

U.S. officials and policymakers often share a long tradition of refusing to acknowledge strategic errors, or to place specific blame on individuals responsible for their authorization and execution. Rather, the causes of defeat are assigned to anonymous sources like "the bureaucracy," "lack of public will," or maybe "Congress." When serving or retired officials are asked whether a war or military intervention was a mistake, they often reply: "That's for historians to decide." Even then-Secretary of Defense Robert Gates said this when asked if Iraq was "worth it" just before he retired: "[I]t really requires a historian's perspective in terms of what happens here in the long term."

But historians do not make future policy decisions; they study and assess previous ones. Sending Marines to Lebanon for such an imprecise and unachievable end-state was a tremendous mistake. Reagan's decision to tacitly admit that it was a U.S. foreign-policy failure, and to then undertake corrective actions, was an admirable trait rarely seen in poilcymakers or presidents.

MIKE SARGENT/AFP/Getty Images