The rising pressures of urbanization in fragile and conflict-affected countries have increased concerns about the vulnerability of cities to armed threats. Changes in the character of armed conflict during the twenty-first century and its effects on cities in the developing world have exposed gaps in the planning and practice of peace and security, which retain a "nation-State bias" that circumvents local perspectives and agencies. Whereas full-scale use of military power in cities remains as destructive today as it has ever been, international organizations such as the United Nations have called for changed approaches to State tactics in urban areas. Mechanisms designed to prevent conflict or to help countries transition back to peace are particularly key if massive human and economic damages are to be avoided in a world of increasingly dense cities. Another key concern is the vulnerability of developing-world cities to low-intensity, if protracted, forms of violence by non-State actors, particularly in post-conflict contexts.