The lesson of Vietnam is how completely it has been forgotten

Bill Clinton is determined to visit Vietnam this autumn, shortly after the election of his successor on 7 November. Despite his conclusively lame-duck status, it will be a remarkable journey: the first trip by a US President since Richard Nixon dropped by for a few hours in 1969 to rally the troops, and a voyage of reconciliation by a man who opposed the war and evaded the draft. But what is most remarkable is how unremarkable the whole venture seems.

Exactly 25 years ago, we watched as last marines were plucked from the roof of the American embassy in Saigon as communist mobs began to ransack the building. It was the biggest military humiliation in America's modern history. Yet where today to seek that maddeningly elusive creature, the "legacy of Vietnam"?

There are the obvious places of course: among the bereaved families of 58,000 Americans and more than 2 million Vietnamese who died; in the still disfigured landscapes of south-east Asia, defoliated by the likes of Agent Orange; and at that haunting, infinitely melancholy memorial in Washington to a war that should never have been fought. But 25 years on, in geopolitical terms, the conflict might never have been.

Consider what Vietnam did not do. It did not alter the outcome of the Cold War. It did not end the role of the United States in Asia; today the US is as much - probably more than ever - what Bill Clinton likes to call the "indispensable power" in the region, a counterweight to Chinese expansionism and the crucial ally of Japan, the Philippines, South Korea and all the other dominoes, as they were then regarded, that did not fall.

Neither did Vietnam herald a new isolationism. Nor, in the longer term, did it shake America's confidence in its values one whit. Each of these fears was widely voiced at the time. Not one of them came to pass. Instead, a quarter of a century after the last helicopter abandoned Saigon, Americans' faith in their system, and in the universal relevance of that system, is greater than ever. And you can't blame them. The loser in Vietnam now dominates the world, economically and militarily, as never before.

But why has Vietnam, the longest war America has fought in 50 years, which destroyed one, perhaps two, presidents and consumed so much life and treasure, proved a mere blip on history? One answer, trite but true, is that unlike Britain, America is not given to wallowing in its defeats. You learn the lessons and you move on. Much of what self-doubt the war did create was banished by Ronald Reagan, that unrivalled purveyor of the feel-good factor.

A deeper explanation, however, is precisely the reason demonstrators around the world protested against Vietnam with such fury. They realised what presidents Johnson and Nixon did not: that this war at bottom was not one about containing communism but about securing a country's national independence.

At the time the confusion was perfectly understandable. Looking back, 1975 may have been the high-water mark of Soviet power. As Saigon fell, Moscow was carrying its rivalry with the West into proxy wars in Africa, while the Helsinki accords of that year formally acknowledged Soviet dominance of eastern Europe. At home, under Leonid Brezhnev, the Soviet economy had yet to betray the first visible signs of decay.

But the North Vietnamese (nor protesters like Bill Clinton for that matter) didn't see it that way. What Hanoi saw was the unfinished business of a 30-year struggle for independence, first from the French and then from the Americans. This was why the other Asian dominoes didn't fall. Vietnam might have been on the front line in the global conflict with communism, but ultimately nationalism, not ideology, was the conflict's driving force. America, the protesters said, had no business there, period.

Today Vietnam has lost its last powers to divide. Only the veterans, physical reminders of recent history, shunned by a nation that wished to move on, had been left outside the fold, their cause kept alive only by crazy theories that missing US servicemen are being held prisoner to this day in jungle camps. Now John McCain's brief but surprisingly popular bid for the presidency this year has helped America come to terms with them too: if McCain, decorated war hero and a PoW himself for five and a half years, bore no grudges, why could America not forgive and forget as well?

Yes, the war has a legacy in the greater assertiveness of Congress over foreign policy and in the doctrines of the Pentagon. Never again, surely, will a president be able to take the country to war, and then escalate that war, without Capitol Hill having a large say at every stage. For the military planners, the lesson is that once the country decides to go to war, it should do so with overwhelming force to minimise casualties and wrap matters up as quickly as possible.

But even that philosophy is now being honoured in the breach. The Gulf War against Iraq, presented as a defence of the security of American and Western oil from a belligerent tyrant, met the post-Vietnam criteria. But Bosnia and in particular Kosovo did not. Although no conceivable US national interest is involved, American troops may be in the Balkans for years, and American lives may be lost.

And like Vietnam, the wars against Slobodan Milosevic have been "liberal" wars, conducted by Democrats. Had Mr Milosevic not caved in, for reasons yet to be satisfactorily explained, Bill Clinton might have been forced along the same deadly path as Lyndon Johnson, of sending in ground troops into comparably awkward terrain to do the job the cruise missiles and smart weapons - those 1990s successors of B-52 carpet bombings of the 1960s - could not. Just as one supposedly noble idea, the containment of communism, justified Vietnam, another, that human rights abuses against ethnic Albanians could not be allowed to stand, underpinned the US-led Kosovo war.

In that sense too Vietnam, with its once immutable lessons for American politicians of future generations, is being forgotten. Bill Clinton's successors will do well to remember that those who forget history are condemned to repeat it.