“We don’t have a dog in that fight.” James Baker, U.S. secretary of state, June 1991, speaking of the impending dissolution of Yugoslavia.

“We don’t exclude territorial adjustments. … We think they’ve got to solve it for themselves.” John Bolton, U.S. national security advisor, August 2018, speaking of talks on territorial swaps between Serbia and Kosovo.

When the next history of the Balkans is written, these two statements will prove to be the most consequential by any U.S. officials. It was James Baker’s statement that gave the green light for Slobodan Milosevic to unleash the full arsenal of former Yugoslavia on breakaway Croatia and Bosnia and Herzegovina. A calamitous, decadelong series of conflicts in the region—all almost wholly avoidable—was the result.

John Bolton’s statement now threatens to undo the ensuing two decade-plus international effort to make peace. Building on rumors about private talks between the leaders of Serbia and Kosovo to swap territory as a means of ending their standoff, and hints of a change in U.S. policy, Bolton has now given the green light to Serbia and Kosovo to trade territory as a way of ending their decadelong—in fact, centurylong—standoff.

In fairness to Bolton, territorial exchange has an alluring logic: Serbia and Kosovo are deadlocked over the latter’s independence, with European Union-led normalization talks going nowhere; neither country can advance to EU membership until the deadlock is addressed; and each country has adjacent bits of territory populated by the other, i.e., Serbs or Albanians who would rather live among their kindred population. So, if the parties can agree on territorial exchange as a way of unblocking their standoff, why should the United States or Europe stand in the way?

The answer is that the logic of a deal between Serbia and Kosovo—if it could be accomplished (and the obstacles are more complex than realized)—cannot be contained. The same alluring appeal of allowing unhappy people to depart one ethnically mixed country for a homogenous one also intrigues the Serbs of Bosnia, the Albanians of Macedonia, and pretty much every minority in the region with an axe to grind and a population concentrated enough to advance a bid for territorial secession.

Unfortunately, in Bosnia’s case, there is no plausible way to divide the country without reigniting war. The country’s Bosniak plurality would never acquiesce in the loss of territory in the east of the country. This area, which includes Srebrenica, is precisely where the prewar majority-Bosniak Muslim population was most brutally “cleansed.” At the same time, no Serb leader could return this territory, which borders Serbia and is now, after wholesale ethnic cleansing, dominated by Serbs.

And even if it were possible to agree on a division of Bosnia, the results are unappealing. Unlike with any other ethnic group in the region, it is religion that most distinguishes Bosniaks from their neighbors. Heavily influenced by Turkey and other dubious Middle East actors, the post-division Bosnia might or might not remain secular. It would almost certainly be landlocked, since the country’s Croats would insist on following their Serb countrymen into secession.

Given the relatively high percentage of Islamic State recruits from the region, and the fact that many of them are poised to return, Bolton and other agnostics on territorial exchange should consider the most likely Kosovo-to-Bosnia scenario: the contentious, possibly violent creation of an economically challenged state in the heart of Europe, subject to Islamist influence, and infused with suffering and abandonment as its defining characteristics.

The chain reaction of events is entirely plausible. Mere discussion of territorial exchange by the likes of Bolton and senior European officials is enough to tantalize Bosnian Serb leader Milorad Dodik, who has long spoken of—and taken preliminary steps toward—secession. Indeed, Dodik cited Kosovo’s 2008 independence as the reason for advancing the cause of separation. In turn, his antics have inspired Croat leaders to agitate for a “third entity,” another relic of Bosnia’s messy war. Croat and Serb grievances may be real. The resort to territorial solutions is, however, simply a precursor to renewed fighting. In short, the seductive logic of territorial swaps over Kosovo inexorably morphs into the logic of war when applied to Bosnia.

The same is true in Macedonia, with an additional international complication. The country’s sizeable Albanian minority, between a quarter and a third of the population, nearly fought a war with the ethnic Macedonian majority in 2001. Albanians of Macedonia are intimately connected to their kin in Kosovo; indeed, for many Albanians, the international border is nonexistent. No matter the pledges by Albanian leaders in Macedonia to remain in the country, the logic of secession will return, particularly once the new, ethnically homogenous Kosovo joins up with Albania. Why would restive Albanians of Macedonia wish to remain outside the Greater Albania fold and, instead, remain locked in a chilly relationship as a permanently designated minority?

As in Bosnia, dividing Macedonia is also a complex, destabilizing affair. Not only would Macedonians and Albanians squabble over the terms—a sizable number of the latter live in the capital, Skopje—but even an agreed division wouldn’t last. The emergence of a rump Macedonian state would immediately open up competition among Bulgaria, Greece, and Serbia for the spoils—reviving the Second Balkan War of a century ago. And as in that conflict, whatever division of the spoils is devised, it will leave one or more parties—including the Macedonians themselves—dissatisfied. Again, territorial division will alter or ignite conflict, not extinguish it.

The timing of Bolton’s policy statement is ironic. Washington helped midwife the recent breakthrough between Greece and Macedonia that can actually resolve century-old tensions—without resorting to territorial division. The two sides made historic and far-reaching concessions, a reminder that painful compromise—the essence of true peacemaking—is possible. The carefully drafted, comprehensive July agreement on Macedonia’s name still faces intense political opposition in Greece and Macedonia, which holds a referendum on it this month. Unfortunately, Bolton’s untimely remarks about Kosovo have injected new uncertainty, encouraging those who would like to torpedo the deal.

In their zeal for a simple solution—a few slight changes to a two-dimensional map—proponents of territorial division also neglect the third dimension: the human cost to the minorities left behind. The presumed exchange on Kosovo revolves around three Albanian-populated municipalities in South Serbia (Presevo, Bujanovac, and Medveda) and three or four Serb-dominated municipalities in Kosovo’s north that are contiguous with Serbia (Lipjan, Leposavic, Zubin Potok, and parts of Mitrovica.)

But there’s an important difference between these two sets of towns: far more Serbs would find themselves on the “wrong side” than Albanians. The relative majority of Serbs who now live in Kosovo’s south—whose status is already marginal—would face outright extinction. The tenuous protections Serbs there enjoy now, enshrined in Kosovo’s Constitution as the price for independence, would become meaningless. Without the promise of recovering the Serb-controlled territory in the north, the entire basis for these special minority protections, imposed by the international community, would disappear. If the majority Albanians don’t rip up those facets of the constitution right away, they would almost certainly give them no more than the barest lip service, no matter the exhortations of the EU or United States.

It is for this reason that Father Sava, the well-known longtime Serbian Orthodox prelate at the magnificent Decani monastery in Kosovo, and other prominent Serbs in Kosovo’s south are vocally opposed to a swap. They know that not only will it spell the end to a Serb future in Kosovo, but it will also erase the historical presence, particularly when it comes to the most treasured elements of Orthodox patrimony there. And when, inevitably, Serb property is seized or breathtaking frescoes are vandalized or destroyed, it will again revive mass Serbian resentment against their Albanian neighbors.

In other words, Serbian President Aleksandar Vucic faces serious dilemmas in executing a territorial swap with his counterpart in Kosovo, Hashim Thaci—and not only in Kosovo itself. A substantial portion of the population in South Serbia is ethnically Serb, including a majority of Medveda municipality, which presumably would be included in a swap. What’s more, a vital north-south highway, known as Corridor 10, slices through these three municipalities. Trading away the highway to Kosovo would mean the loss to Serbia of its southern access to the sea, through Macedonia and Greece. Building an alternative route would be prohibitively expensive. With the loss of proprietary access to the sea through Montenegro, the volume of trade, and the heavy Chinese infrastructure investment that promises to benefit Belgrade, it is unimaginable that Vucic would give away Corridor 10.

On the other hand, if Thaci allows Vucic to keep the highway, he risks being pilloried by his opposition. The three northern municipalities that Serbia covets contain the strategic Trepca mine. Thus, the putative deal would have Thaci both ceding a Kosovo strategic asset (the mine) to Serbia, while allowing Vucic to keep one (the highway). Unlike Vucic, who towers over his rivals, Thaci has a far more tenuous political standing. It is questionable whether he could ever sell such a deal in exchange for United Nations membership and mutual recognition.

The way out of this mess is for Bolton and the Trump administration is to do as they pledge and stand up for U.S. interests. Instead of letting spineless Europeans off the hook or being goaded by a couple of tinhorn Balkan leaders into cutting a destabilizing arrangement, Washington should stand firm. U.S. leaders should join forces with Berlin, where Chancellor Angela Merkel has denounced the proposed territorial swap concept, and insist that Serbia and Kosovo—as Greece and Macedonia have just done—work through the difficult issues and come up with solutions that don’t rest principally on territory. The fact that Belgrade and Pristina are even talking about territorial swaps is, itself, recognition that the time to cut a deal is nigh. Appointing an EU special envoy for Kosovo and Serbia (with whom Washington would collaborate) would send an important signal.

If the parties nonetheless insist on making territorial exchange the centerpiece of their negotiations, then the United States and Germany can work together contain the consequences. These three conditions will make even the most short-sighted proponent of a territorial swap to think through the implications:

First, there can be no deal on swapping Kosovo territory until negotiations on the Dayton Agreement Constitution for Bosnia are reopened and concluded. The West cannot afford to allow a reckless deal on Kosovo to destabilize the country that saw the bloodiest fighting. Belgrade, which is a co-signatory of the Dayton Agreement, must first engage with its Serb brethren and guide them to negotiating the long-awaited fundamental reforms that will finally make Bosnia functional.

Second, the parties must accept the principle that no territorial exchange can occur without a “majority of the minorities,” that is, a referendum requiring majority approval by those left behind under a proposed territorial swap.

Third, there must be extraordinary arrangements for new EU entrants, like Serbia, that prevent it from impeding the entry of any other state in the region. It is imperative that Belgrade not be in a position to renege on pledges to Kosovo, which will not be in a position to join the EU for many years. The EU will also have to insist that the five members that don’t recognize Kosovo will do so in the wake of a Belgrade-Pristina territorial swap.

No one should insist that the peoples of the Balkans have to like each other or even that they have to live with each other. But if leaders pursue territorial separation as a way of overcoming conflict, they must do so in a way that will not create even more problems.