Nationalism is arguably one of the most detrimental peace-breaking factors in conflict-affected societies. This article examines how ethno-nationalist elites, subterranean movements, and ordinary people can become blockages to sustainable peace and reconciliation after violent conflict. It argues that peacebuilding and state-building imposed from outside as conflict transformation approaches without acceptable peace settlement and resolute solution of the disputes among parties in conflict risk enabling the co-optation of power-sharing arrangements by ethno-nationalist elites, contestation of peace and reconciliation by subterranean mono-ethnic movements, and the occurrence of vernacular peace-breaking acts. This negative mutation of nationalism not only harms peace, justice, and development but also undermines the rights and needs of distinct identity groups. Under these conditions, escaping the nationalism trap in conflict-affected societies requires seeking political change through post-ethnic politics and reconciliation through everyday pacifist acts undertaken by the affected communities themselves. The article draws on Kosovo to illustrate empirically the dynamics of peace-breaking and practices of everyday nationalism. It seeks to bridge debates on nationalism and post-conflict peacebuilding and offer alternative pathways for rethinking strategies of peace in divided societies.