One year after the end of the Bosnian war, there are fresh political upheavals in former Yugoslavia - but this time the upheavals may bring a brighter future for the people of this long-troubled region of Europe. The daily street demonstrations in Belgrade against President Slobodan Milosevic of Serbia, and recent protests in Zagreb against President Franjo Tudjman of Croatia, show that an increasingly large number of Serbs and Croats want a change from the diet of authoritarian nationalism on which they have been fed throughout the 1990s. The demonstrators want democracy, an end to official corruption, media free of state control, and civil rights - in short, everything that people elsewhere in Eastern Europe won in 1989, but which Mr Milosevic and Mr Tudjman correctly regard as threats to their personal authority.

It is no coincidence that the popular challenges to the strongmen of Serbia and Croatia have arisen since the end of the 1991-95 wars in former Yugoslavia. During the conflicts, only a minority of brave individuals dared raise the banner of criticism and take the risk of being branded as traitors by their rulers. Today, a Serb or Croat who demands political reforms and civil liberties cannot be accused of jeopardising his country's existence, for the wars are over and the Serbian and Croatian governments no longer have the right, if ever they did, to insist on meek submission to authority in the name of national unity.

Predictably, the ruling parties in Belgrade and Zagreb - the Socialist Party of Serbia and Croatian Democratic Union - have reacted to the popular unrest by condemning "foreign interference" in their countries' internal affairs. How often we used to hear such growling from the likes of Nicolae Ceausescu, Erich Honecker and Gustav Husak in the Eastern Europe of the 1980s. Little good did it do those small dictators, and little good will it do Mr Milosevic and Mr Tudjman, for the fundamental pressure for change is coming from within their societies, not from outside.

In Serbia, the street protests were triggered by the transparently unfair decision of the authorities to annul municipal election victories for the opposition Zajedno (Together) Coalition in Belgrade and other large towns. But the popular discontent had deeper roots, lying in years of economic mismanagement, social hardship and the perception of the ruling elite as a group that has enriched itself in the company of war profiteers and gangsters. Even if Mr Milosevic ultimately allows the opposition to take power at local government level, the pressure for reform is unlikely to disappear.

In Croatia's case, about 100,000 people demonstrated in Zagreb last month in protest at the government's decision to ban the city's only independent radio station. Although the government soon reversed the decision, its attempts to muzzle freedom of expression have been one of the most consistent and least attractive features of Mr Tudjman's six years in power. Like Mr Milosevic in Belgrade, he has also dug a hole for himself by refusing to recognise an opposition victory in municipal elections in Zagreb.

Far from sponsoring popular protest in Serbia and Croatia, Western governments have, if anything, displayed considerable caution in expressing support for the pro-democracy forces in Belgrade and Zagreb. Their message seems to be that democratic change would be welcome, and that violent repression of the opposition would certainly be unacceptable, but that other factors need to be kept in mind. This refers above all to the supposedly crucial role of Mr Milosevic and Mr Tudjman in keeping Bosnia at peace.

But are the two leaders really doing all they can to uphold the Dayton peace settlement for Bosnia? As was made clear during this week's conference on Bosnia in London, Mr Milosevic in particular seems to have nothing but contempt for one of Dayton's central provisions - the capture of indicted war criminals and their transfer to the United Nations tribunal in The Hague for trial. For all his disputes with the Bosnian Serb leadership, there is little doubt that Mr Milosevic could exert pressure in the necessary direction if he so chose. As for Mr Tudjman, he continues to support separatist Bosnian Croats who wish to merge with Croatia rather than make a success of Bosnia's Muslim-Croat Federation. The Bosnian Croats' mini-state, Herzeg- Bosnia, was officially abolished last summer, but continues to exist in practice, flying the Croatian flag and using the Croatian currency. There is every reason to suppose that Mr Tudjman still harbours a vision of a Greater Croatian state.

The year-old peace in Bosnia is like the proverbial glass which, depending on one's perspective, is either half-full or half-empty. The peace has held, and that is partly because the Serbian and Croatian leaders have helped to keep it. But the peace is also fragile, and that is because some of their policies continually undermine it.

Western governments should recognise that a change of leadership in Belgrade and Zagreb would not necessarily jeopardise the Dayton settlement. The Serbian and Croatian oppositions are clear that they support peace in Bosnia. Anything less, and they know that they would be pariahs on the international stage.

More broadly, it would surely be desirable to see less nationalistic, less authoritarian governments in Serbia and Croatia. Perhaps Mr Milosevic and Mr Tudjman have it within themselves to change. But the more they prove themselves unwilling to abide by European standards of democracy and civil liberty, the less they deserve to be propped up by us.