Mehmedovic has begun rebuilding his house with donated materials–under the watchful eyes of American troops. “The windows and doors just arrived,” he tells Stapleton, as the lanky commander nods in approval. “The coal came last week. Everything is good.” Climbing back into the Humvee, Stapleton takes a bite of a sugar doughnut and a sip of coffee. “So few people are coming back to this area,” Stapleton tells a visitor. “The only reason they feel safe at all is because we’re here.”

The question is, how long will they remain? The Bush administration has made no secret of its desire to withdraw U.S. peacekeepers from the Balkans and let European troops take over the job. In December the new head of the U.S. National Security Council, Condoleezza Rice, assured Wolfgang Petrisch, Bosnia’s chief international administrator, that the Bush team would not move hastily; they would phase out American involvement–and only in consultation with European partners. But even the possibility of U.S. disengagement is alarming to many Bosnians and others in the Balkans. They say that the country’s fragile peace could collapse without U.S. support. American troops on the ground agree. Abandoning Bosnia, they say, would invite violence by ethnic extremists on all sides, and gravely damage America’s credibility with its allies. “We can’t just say, ‘Let’s divorce ourselves from NATO’,” says Maj. Gen. Walter L. Sharp, commander of the U.S. forces in Bosnia.

Five years after the Dayton peace accord, Bosnia has made some progress toward stability. Unlike Kosovo, Bosnia has functioning local governments and has kept a lid on ethnic violence. But it is still divided into two mutually suspicious entities, the Muslim-Croat Federation and the Republic of Srpska, and all three ethnic groups are effectively led by the same nationalist parties that held power during the war. Cities and towns remain sharply split along ethnic lines; almost all schools are segregated, and 800,000 internally displaced people still haven’t returned home. Suspected war criminals hold key positions of power in the police and local government, especially in the Republic of Srpska. “Bosnia is a thin facade held up by a framework of international support,” charges James Lyon, director of the International Crisis Group, a human-rights watchdog organization, in Sarajevo. “If we pull out tomorrow, everything would collapse.”

American peacekeepers say they’re working hard to prevent that collapse. The United States now has 3,900 troops in Bosnia, down from 18,000 five years ago, all based in the northeast sector of the country. The soldiers conduct demining operations (13 Bosnians were killed by mines last year), inspect weapons-storage sites and run a program of voluntary arms surrenders among the civilian population known as Operation Harvest. They also monitor the International Police Task Force, a United Nations-supervised outfit whose 1,500 unarmed police, mostly from Asian and African nations, train local cops and assist in investigations. A civil-affairs unit meets regularly with local mayors, oversees school construction and ensures adequate supplies of water and coal to returnees. “Our mission is to keep the Bosnian armed forces contained in a box, and get civil institutions to take over running the country,” says Sharp.

The peacekeepers also contribute in less tangible ways. The U.S. military runs 100 patrols a week, showing the flag across eastern Srpska–where hard-line Serbs still try to block the efforts of Muslims to return home. Seven days a week, Stapleton, a high-school history teacher in his civilian life, and a half-dozen other North Carolina guardsmen attached to the 134th Armored Division don helmets and Kevlar body armor and patrol the region around Srebrenica, where more than 7,000 Muslims were massacred in 1995. Five years of U.S. peacekeeping have made the job routine: guardsmen spend most of the day tossing Super Balls and lollipops to grateful kids by the roadside, stopping occasionally to check on the safety of the handful of recent returnees. Last fall some Muslim returnees complained that they felt threatened by Serb deer hunters who were firing their shotguns in the hills behind their homes. “We stepped up patrols on weekends, talked to the hunters and got rid of the problem,” says Stapleton. In four months of patrols, the unit has never been fired upon. “If we lost a single bullet, that would be a major event,” Stapleton says. Still, he believes that Bosnia remains a tinderbox–and that withdrawing would be a big mistake. “Our presence has a strong psychological effect,” he says.

That’s certainly true in Brcko, a divided town on the Croatian border in the U.S. sector that was the scene of some of the heaviest fighting of the war. Three months ago Serb students staged angry protests over a law forcing them to share their school building with Muslim students; local police kept the demos from escalating into a riot, but the city remains tense. Sulejman Sakic, 46, a Muslim shop owner who returned last year from Tuzla, says that he and his neighbors on Brcko’s outskirts live in fear of the Serbs who control the center of town. “The Serbs tell us openly, ‘Didn’t we kill you? Didn’t we rape you? Didn’t we burn your houses? Why do you want to live with us?’ " he claims. “If the Americans left, the shooting would start again.” Sakic’s neighbor Vahid Tahto, 42, scoffs at the idea that British and French troops can keep things calm. “The Europeans did nothing for us during the war. We don’t trust them,” Tahto says.

That’s a sentiment shared by some international officials in Bosnia. The American peacekeepers, they say, embrace the vision of Bosnia as a multiethnic state; if the U.S. troops leave, “the Europeans might be more willing to accept Bosnia’s permanent division into ethnic enclaves,” says one top official in Sarajevo. That’s a chilling prospect for returnees such as Aljo Mehmedovic, who tries to ignore the insults he hears from the fiercely nationalistic Serbs in his corner of northeastern Bosnia near the Serbian border. If U.S. soldiers withdrew, he says with a shudder, “it wouldn’t be good, because the Serbs haven’t changed. The only reason I came back is because Americans are here to protect us.” Mehmedovic can only hope they stick around long enough to ensure he can live there in peace.