BERLIN -- As Croatian and Muslim armies recently advanced across western Bosnia toward yet another Serbian-held village, continuing the Bosnian war's breathtaking reversal of fortunes, a dark thought occurred to a few United Nations observers: What if, after taking their next objective, the allies turn their guns on each other?
It hasn't happened, but the thought illustrated an important point: The Croat-Muslim Federation, virtually taken for granted in discussions of Bosnia's future, is anything but secure or certain in the minds of its two partners.
Ironically, the greatest dangers threatening the federation have been brought on by military success. By winning back dozens of towns from the rebel Bosnian Serbs across more than 1,500 square miles, Muslim and Croatian armies have raised the hopes of thousands of refugees clamoring to move back home. But Croatian forces occupying a large part of those gains have so far been unwilling to share the spoils.
The town of Jajce is one of the more contentious examples. Around 45,000 people lived in the Jajce area before the war, of which 39 percent were Muslim, 35 percent were Croatian and 19 percent were Serbian. Serbian troops drove most of the Muslim and Croatian residents south in 1992.
Now that Croatian troops have recaptured the town, "they're putting up all the usual sort of Croat paraphernalia and flags and emblems, and the [Muslims] are pretty worked up about it," said Michael Williams, former spokesman for U.N. forces in the region and now an analyst for the International Institute for Strategic Studies in London.
Indeed, the Muslims can't even get into the town; their troops remain encamped on the outskirts.
Similar scenes have unfolded in other newly captured towns, with one side holding the other at arm's length as it claims the place for its own people.
The resulting tensions have begun spilling into peace negotiations. At a meeting with U.S. special envoy Richard C. Holbrooke last week in the Croatian capital of Zagreb, Croatian President Franjo Tudjman and Bosnian President Alija Izetbegovic shouted angrily at each other several times.
Witnesses said there were more acrimonious exchanges than at any meeting the men had held before with their supposed enemy, Serbian President Slobodan Milosevic.
And even in the quietest corners of the federation's territory, in lands governed since March 1994 by a Croat-Muslim cease-fire agreement, people still speak of old scores to be settled.
Dunja Radonic, a young woman working at a cafe in the mostly-Muslim central Bosnia city of Zenica, voiced the feelings of many when she said, "No one thinks that it is really over. Too many people lost someone in their family, or lost their home."
In the central Bosnian village of Ahmici, Muslims have placed a memorial on the edge of the village, a bitter reminder of the day Croatian militiamen gunned and burned their way through the community on a spring morning. No one lives there now. The homes are burned and roofless.
Several nearby Croatian and Muslim villages have their own memorials from 1993, mourning losses not to Serbian aggression but to those inflicted by their current allies.
Late last year the abiding ill feelings seemed on the verge of tearing the federation apart, prompting U.S. and German diplomats to scurry to the rescue. "Every time the civilian authorities would be ready to break [the federation] apart, the military people would jump on them and say, 'You're not going to do anything to damage this,' " the U.N. mediator from the region said. "They had to acquiesce to this arrangement or they would have lost everything to the Serbs."
In some minds, the idea of a Greater Croatia has begun to supplant the idea of a Greater Serbia. If the trend continues, Mr. Williams said, the Muslim forces of the Bosnian government might eventually feel compelled to turn toward the Serbs for protection against the Croats.
And that sort of Orwellian shift could drive the negotiators back to their maps, and the soldiers back to their guns.