By BBC Diplomatic Correspondent Barnaby Mason

For Russia and China and critics of Nato in the West, the bombing campaign was a violation of international law.

Military action was undertaken without the authority of the United Nations Security Council, thus undermining and usurping the UN.

Western governments sometimes argued that various Security Council resolutions did give indirect backing to the air strikes.

But in reality they knew that the Council would never have given specific authorisation, precisely because of the opposition of Russia and China.

The overriding justification was the suffering of the Kosovo Albanians and the need to stop the repression being carried out by Serb forces.

Nato's reputation saved

The fact that the air strikes took nearly three months to have an effect and may have made things worse at the start is a separate point; debate will doubtless go on about whether a different Nato strategy would have been more effective in practice.

In the minds of western leaders, this was a just war, undertaken for humanitarian reasons, not territory or power.

It was in tune with a growing international consensus that national sovereignty has its limits: you can no longer argue that anything that goes on inside a nation state, however appalling, is no one's business but its own.

For the Chinese Government and some others this is a dangerous heresy. But the tide of opinion has been flowing the other way.

International conventions ban certain crimes against humanity and make it possible for the perpetrators to be tried anywhere in the world.

The most dramatic example is the arrest in Britain of the former Chilean dictator, General Pinochet.

To resolve the Kosovo conflict, the West found that it needed the help of Russia - and that meant bringing the whole issue back to the UN.

Javier Solana and Nato: reputation saved

Nato was not in the end able to settle the crisis on its own.

The Security Council has approved the deployment of an international force, but it has not given Nato undisputed supremacy.

The resulting compromise may be messy, like the real world.

For Nato itself, with its credibility at stake, the outcome is better than sometimes looked likely.

The Alliance held together under the strains despite the doubts and the agonising and - in the case of Greece - a hostile public opinion.

New and aspiring members in eastern Europe gave solid support, showing that the future as far as they were concerned lay in integration into the prosperous West.

Some European politicians have gained in stature as a result of the war.

Raised profiles

Schröder (left) and Blair: gained from crisis

The most obvious case is the hawk with the highest profile, UK Prime Minister Tony Blair.

The leaders of the Social Democratic - Green Party coalition in Germany, Gerhard Schröder and Joschka Fischer, took greater risks at home and will reap the benefit.

And the Italian Prime Minister, Massimo D'Alema, faced down domestic opposition and made sure that vital military bases in Italy remained available.

The war could be a turning-point for the European Union as a whole.

If the United States provided the vast bulk of the air campaign, the ground force will be a largely European affair.

In the last week of the war, the EU adopted a common defence strategy which will in due course allow it to mount military operations of its own.

Several factors made the move possible. The Blair government has reversed the UK's long-standing opposition to a military role for the EU.

The French have warmed towards Nato, whose help will be essential. A new generation of German leaders has emerged from under the long shadow cast by the Nazis.

And the Clinton administration has actively encouraged European integration - especially if it means Europe paying more for its own defence.

That is likely to be a crunch point, of course. EU governments are not yet ready to put their money where their mouth is.

The EU cannot be the new Nato

It is decidedly premature to think of the European Union mounting large-scale military operations to combat future crises.

Politicians are well aware that the Kosovo conflict was a close-run thing, which might have ended in disaster.

The EU will not replace Nato, and Nato will not replace the UN.

There will be no consistent policy of intervening military to protect human rights around the world.