But at this point analogies with the 1930s in Europe quickly turn sour. Soviet gains in the Third World in the 1970s and early 1980s were gains along the Cold War's periphery. They did not affect the central balance of military power between the United States and the Soviet Union; on the contrary, those gains quickly turned out to be liabilities. In contrast, Hitler's successes in the Rhineland and Czechoslovakia undermined the European balance of power and sped the planet to another world war. To equate, as [Michael] Lind did in Vietnam: The Necessary War, the Soviet invasion of Afghanistan, to say nothing of Soviet "triumphs" in places like Ethiopia and Guinea-Bissau, with Hitler's occupation of the Rhineland and Czechoslovakia is to dismiss the critical distinction that George Kennan made ... between the center and the periphery. The Soviet invasion of Afghanistan was a strategic dead end in very much the same way that intervention in the Vietnam War proved to be for the United States. Indeed, both interventions reflected not only an overvaluation of the Third World's strategic importance as a whole but also a failure to make key distinctions of importance within the Third World. For the United States, who runs Afghanistan, Ethiopia, and Guinea-Bissau is simply not as important a question as who runs Saudi Arabia, South Africa, and Mexico. Strategically, "dominoes" come in different weights and sizes, and the fall of one here may not matter compared with the fall of one there.

The terrorist bombing that killed the 241 Marines did, in fact, drive the United States from Lebanon, although it would take three and one-half months for events and advisers to persuade Reagan to agree to the withdrawal plan. The withdrawal was steadfastly opposed by Shultz, who continued to believe that U.S. diplomatic interests required the United States to remain in Lebanon. "We are in Lebanon because the outcome in Lebanon will affect our position in the whole Middle East," Shultz testified to Congress on October 24. "To ask why Lebanon is important is to ask why the whole Middle East is important—because the answer is the same."

Weinberger would never see it that way. He thought that Lebanon was hopeless and that the Marines had no useful purpose there. "I've never seen Cap look as sad as he did after the Marines were killed," said Colin Powell. Recalling the NSC debate of the previous Tuesday, Weinberger told Powell, "I wished I had been more persuasive with the president."

The intervention began with the best of humanitarian intentions, but slowly and inexorably the U.S. military was drawn directly into the strife, provoking deadly retaliation by those opposed to the American presence. Lebanon seemed to validate the Vietnam analogy, and it clearly contributed to Secretary of Defense Caspar Weinberger's determination to speak out on the issues of when and how force should be used.

(1) First, the United States should not commit forces to combat overseas unless the particular engagement or occasion is deemed vital to our national interest or that of our allies. That emphatically does not mean that we should declare beforehand, as we did with Korea in 1950, that a particular area is outside our strategic perimeter.

(2) Second, if we decide it is necessary to put combat troops into a given situation, we should do so wholeheartedly, and with the clear intention of winning. If we are unwilling to commit the forces or resources necessary to achieve our objectives, we should not commit them at all. Of course if the particular situation requires only limited force to win our objectives, then we should not hesitate to commit forces sized accordingly. When Hitler broke treaties and remilitarized the Rhineland, small combat forces then could perhaps have prevented the holocaust of World War II.

(3) Third, if we do decide to commit forces to combat overseas, we should have clearly defined political and military objectives. And we should know precisely how our forces can accomplish those clearly defined objectives. And we should have and send the forces needed to do just that. As Clausewitz wrote, "no one starts a war - or rather, no one in his senses ought to do so - without first being clear in his mind what he intends to achieve by that war, and how he intends to conduct it."

War may be different today than in Clausewitz's time, but the need for well-defined objectives and a consistent strategy is still essential. If we determine that a combat mission has become necessary for our vital national interests, then we must send forces capable to do the job -- and not assign a combat mission to a force configured for peacekeeping.

(4) Fourth, the relationship between our objectives and the forces we have committed - their size, composition and disposition - must be continually reassessed and adjusted if necessary. Conditions and objectives invariably change during the course of a conflict. When they do change, then so must our combat requirements. We must continuously keep as a beacon light before us the basic questions: "is this conflict in our national interest?" "Does our national interest require us to fight, to use force of arms?" If the answers are "yes", then we must win. If the answers are "no," then we should not be in combat.

(5) Fifth, before the U.S. commits combat forces abroad, there must be some reasonable assurance we will have the support of the American people and their elected representatives in Congress. This support cannot be achieved unless we are candid in making clear the threats we face; the support cannot be sustained without continuing and close consultation. We cannot fight a battle with the Congress at home while asking our troops to win a war overseas or, as in the case of Vietnam, in effect asking our troops not to win, but just to be there.

(6) Finally, the commitment of U.S. forces to combat should be a last resort.

[W]hen the Bush administration responded to Saddam Hussein's invasion of Kuwait by dispatching U.S. troops to the Arabian Peninsula, key officials went out of their way to show that there would be no repetition of the errors that had led to disaster in Vietnam. There would be no micromanagement, no political meddling, no half-measures, and no quagmire. In that sense, the Gulf crisis of 1990-91 became a test case for the Weinberger Doctrine. Senior civilians, beginning with President Bush, and senior military officers, led by Powell, made a concerted effort to portray Desert Shield and Desert Storm as military campaigns designed and conducted with Weinberger's admonitions in mind.

That the war ended in military victory, cheaply and quickly won, seemingly validated Weinberger's approach. As principal steward of that approach and chief military architect of victory, Powell himself acquired enormous additional standing with the public and the press, so much so that in the media the Weinberger Doctrine was promptly eclipsed by a nearly identical Powell Doctrine. That Powell's own frequently expressed convictions—above all a belief in overwhelming force employed decisively on behalf of vital interests—would henceforth constitute "the American way of war" seemed all but self-evident.

Viewed in isolation, the U.S. military response to each of these wildly disparate situations suggested an administration flying by the seat of its pants, relying on improvisation rather than principle. That perception was not entirely without merit. If by its actions the Clinton administration showed that it had discarded the Weinberger-Powell guidelines for using force, neither the president nor any of his chief lieutenants made any apparent effort to articulate a replacement. There was no particular speech or authoritative document promulgating an official Clinton doctrine.

Whatever the utility of reasoning by historical analogy as a tool of policy formulation and implementation, it is clear that policy makers will continue to be influenced by past events and what they believe those events teach. It is also clear that presidents' knowledge of history varies widely, and that reasoning by historical analogy is but one of a host of factors at play in presidential decision making. Presidents Theodore Roosevelt, Woodrow Wilson, Harry Truman, and John Kennedy were well read in history, whereas presidents Lyndon Johnson, Ronald Reagan, and George Bush [the elder] displayed considerably less knowledge of history. Moreover, in analyzing a specific presidential use-of-force decision it is virtually impossible to determine the exact influence of reasoning by historical analogy in relation to such other factors as presidential personality, domestic political considerations, and the role of key advisers. Munich clearly weighed heavily on the minds of Truman in 1950, Johnson in 1965, and Bush in 1990, as didVietnam on the mind of Clinton in the 1990s. But all the evidence suggests that, for better or for worse, some thinking about history attends all significant presidential uses of force, especially those that invite war.