As a schoolchild I learned the poem "In Flanders Field." Today, as U.S. ambassador to NATO, I will be standing at a ceremony in Flanders. The wreath will be laid, shots fired, "Taps" played. Why did these men fight and die?

If we are to prevent World War III, we must understand how we could have prevented World Wars I and II. In my opinion, two great villains are responsible: uncertainty and miscalculation. Unclear alliances, secret agreements and differing perceptions led to tragic miscalculations.

In the summer of 1914, not one European leader believed that a worldwide catastrophe would result from his decisions. There had been earlier Balkan crises in 1908 and 1912. They had been resolved without major power conflict. Russia had backed down. Some commentators said trade relationships made war impossible. The kaiser believed that Britain would not respond to the violation of Belgian neutrality. But there were too many ambiguous commitments and secret agreements, and war came.

Many historians argue that World War II was a product of Hitler's calculated actions. I disagree. Hitler wanted conquest without war, at least without major war. Having seen the democracies back down over Germany's rearmament, Austria's annexation, the Sudetenland, Czechoslovakia and then Munich, Hitler reasoned quite naturally that they would back down again over indefensible Poland. In 1939 the history of 1914 was repeated through a series of miscalculations stemming from a lack of clear commitments by democratic alliances.

NATO represents unambiguous commitments and credible deterrence. Dean Acheson once said that NATO was "not an improvisation. It was born out of the facts and lessons of history." The founders of the Atlantic Alliance were determined to avoid the mistakes that had catapulted the world into two wars. If ambiguous commitments led potential aggressors wrongly into believing they could successfully use or threaten to use military power, then an unambiguous commitment would be the centerpiece of their new alliance.

The idea of war in this year of 1986 is remote. After 40 years of peace in Europe, influential Americans -- some neoconservatives on the right, some revisionist historians on the left, some in a quandary over Gramm-Rudman-Hollings budget cuts -- want to set off a process that would take us out of Europe.

"Time to let Europe build its own defense," one reads on the op-ed page of The Wall Street Journal. In the wake of the initial lack of European support for the U.S. action against Libya, a country outside the NATO area of defense, a distinguished editor writes, "what starts with the withdrawal of American tourists ends in the withdrawal of American soldiers." Another commentator ominously notes: "The cost of defending Japan is fuzzier to calculate, but it would be hard to figure less than $150 billion for Europe and Japan together. And guess what? That's just about the size of the deficit." Others say NATO can't act, that it is a constraint on our other commitments around the world.

Today I will gaze on those white crosses in Flanders Field. Fifteen million died in World War I. Fifty million in World War II. Oh, but it would never happen again, say our new isolationists. Some left-wing revisionist historians say there is no threat anyway, that we caused the cold war in the first place. Some neoconservatives say the Soviets stalk us elsewhere, that there is no danger in Europe. Reduce the commitment to Europe, toss out Article V of the North Atlantic Treaty; the Pacific basin is what counts anyway.

The Soviets have been unsuccessful in splitting Europe from America. But their purposes remain constant. Having been dealt setbacks from the Berlin crises to the deployment of intermediate-range missiles, the Soviets know that their huge conventional superiority in the 1990s, when nuclear weapons will not have the deterrent value of earlier years, will give them new opportunities. They may reason that blackmail could work, that they could achieve their purposes without war, or without much of one. They would be encouraged in this by the fraying of the American commitment.

This same fraying would introduce precisely those elements of ambiguity and uncertainty that had such deadly effects in 1914 and 1939. "If ye break faith with us who die, we shall not sleep, though poppies grow in Flanders Fields." The writer of these lines, Canadian Dr. John McRae, treated patients who were rolled down a bank into his station. He could not have known the consequences of a war in our time. Even to us they are scarcely imaginable.