“You are looking at your own future here,” said Adnan Huskic, a scholar in politics and international relations at the School of Science and Technology in Sarajevo. “We have been dealing with the rise of nationalist populism for years.”

Instead of creating a unitary state, the 1995 agreement that halted the bloodletting in Bosnia — reached in Dayton, Ohio by the leaders of Bosnia, Serbia and Croatia — only entrenched the nationalist elites that prosecuted the war. It divided Bosnia into two “entities” — a Serb-run Republika Srpska and a mixed Muslim-Croat Federation of Bosnia and Herzegovina. At the summit of this ramshackle state stood the presidency, controlled by three elected presidents, one each for Bosnian Serbs, Croats and Muslims, who are known as Bosniaks.

Authority was further subdivided, largely along ethnic lines, with the establishment of 10 local units of government called cantons, each with its own president and set of ministers who duplicate many of the functions of the weak national government.

Mr. Golos, the Muslim firefighter, said he has many friends across the ethnic boundary and feels no enmity toward Serbs, who started the fighting but have now mostly left the city, or Croats, who rained artillery shells and sniper fire into his neighborhood during the war.

But he worries that, instead of fading, wartime divisions have only hardened. Because of largely segregated schooling, a postwar generation of young Croats and Bosniaks, Mostar’s two main ethnic groups, often know only members of their own group and have little or no shared experience.

“We have moved backwards, not forward,” Mr. Golos said.

His 20-year-old daughter, Amila, attended high school in the same building as Croat students but never mixed with them because students went to classes in shifts — Muslims from 7:30 a.m. and Croats from 2 p.m., a common arrangement in Bosnia.