Leading Article: Saved by Uncle Sam - but what about next time?

"You can always count on the Americans to do the right thing," said Winston Churchill, "after they have exhausted all the alternatives." This week, the old adage proved true again, when belated US intervention brokered a peace deal in Bosnia. At last the Americans showed some leadership, but only after they and their European partners had dithered for the best part of four years.

It was, in the end, the Americans who made the difference. This was the first major war in mid-Europe since 1945. It was a war that saw the return of concentration camps and genocide. Yet the Europeans, with their petty, national concerns, demonstrated that they were not up to the task of settling the conflict. The development of the European Union and other international institutions may suggest that the bad old days of nationalist rivalry have been replaced by co-operation. But the Bosnian debacle has illustrated Europe's inability to act in concert on security issues. We are not yet ready to shake off 50 years of dependence on Washington.

The problems that stand in the way of common European action remain significant. The United States may be gridlocked by the separation of powers, but at least it is a single nation state with a common language. Europe is badly handicapped by having several languages and by each nation jealously guarding its own sovereignty.

In Bosnia, President Clinton arrived with his cavalry in the nick of time. Matters had seriously deteriorated: the conflict had left Britain and France more estranged from Washington than at any time since the Suez crisis in 1956. Like Roosevelt before him in the Second World War, President Clinton was portrayed as successfully resisting isolationism within the US Congress. He offered the resources of the New World to sort out the problems of the Old. In the process he, at least temporarily, bolstered Nato, a shaky edifice which the Bosnian issue might easily have destroyed. The US holds up Nato like a tent pole, while other nations provide the pegs. Without the pole, the tent would collapse.

So are we now back to normal? Does the settling of the Bosnian war and the manner of peace-making mean that the North Atlantic relationship is once again secure? Have political analysts been wrong to predict that, with the end of the Cold War, the United States, captivated by economic growth in the Pacific Rim, will desert Europe for Asia?

Europe clearly still needs the US commitment, which is enshrined in Article 5 of the North Atlantic Treaty and marked by the presence of over 100,000 US troops on the Continent. The Americans in effect subsidise Europe's defence to the tune of $90bn a year. We have struck a bargain with them: they patrol our territory and in exchange give us access, via Nato, to their huge stockpile of equipment, their transport capacity and their ability to gather intelligence. It's a cheap deal for Europe.

But is it reliable? The Americans still have much to gain from close involvement across the pond. After all, the European Union is still America's most important trading partner. And although the Cold War is over, US fears about potential threats from the east remain. No one knows how aggressive the Russians could prove to be: elections there next month could offer some indication. With Poland electing a neo-communist president this week, it is unclear where the dividing line between east and west will be drawn. So a large-scale withdrawal from Europe would be against US interests.

But Europeans would be foolish to think that the Bosnian agreement has resolved American ambivalence towards military engagement in Europe. The Republican-controlled Congress is determined to leave the Continent to its own devices. Indeed it was the action of Congress, in calling for an end to the arms embargo imposed on the Bosnian Muslims, that forced Clinton to intervene.

An end to the embargo would have required a withdrawal by the United Nations, which Clinton had promised to back up with 25,000 US troops. Had he kept that promise, he could have found himself going into election year with a potential foreign policy disaster on his hands.

In short, Bosnia was a special case. The White House was galvanised largely by domestic considerations into offering leadership. The president wished to avoid being accused of wasting taxpayers' dollars and risking American lives in a country about which voters know very little. This is the Clinton style: he does not have a grand vision of what to do abroad - he has a re-election strategy. When he arrives here next week, we will once again see his parochialism, how domestic concerns drive his foreign policy. Keen to garner Irish-American votes, he will do all he can to secure some movement in Ulster's peace process.

American intervention in and commitment to Europe, despite the Bosnian episode, remains uncertain and fragile. This is a sobering thought. For parts of Europe remain potential scenes of violent conflict. And there is no reason to believe that next time Europe will do any better than its ignominious performance in Bosnia. Waiting for President Clinton to have the time and inclination to step in is both risky and an abdication of responsibility. It cost hundreds of thousands of lives in former Yugoslavia.

To date, the Europeans have done little to address this source of instability. They have made scant progress on developing a separate nuclear umbrella, which would be founded on the weapons held by Britain and France. Co-operation on defence matters is in its infancy, undermined by the anti-federalism that is growing in member states of the European Union. As a result, the only option is to prop up a weakened Nato relationship whose life expectancy is unclear.

The Bosnian episode has shown how much Europe still needs the United States, even in its own back yard. The problem is that there is no guarantee that, in future, the United States will be prepared to act.