In the last decade of the bloodiest century in recorded history, the United Nations devised a new instrument—preventive deployment—to deal with the age-old problem of war. This unique first-hand study provides the definitive account of the United Nations Preventive Deployment Force (UNPREDEP), which was deployed from 1992 to 1999 in Macedonia, for the first time before hostilities erupted. Abiodun Williams explains why UNPREDEP was established, how it implemented its new mandate, and its pathbreaking accomplishments. Placing his account in the context of the evolution of UN peacekeeping and Macedonian history, Williams’s analysis is grounded in systematic empirical detail. The book demonstrates that UNPREDEP enhanced the stability and security of Macedonia, as well as provided international political legitimation of the country’s sovereignty and independence. Preventing War makes a strong argument for the wisdom and efficacy of preventive action and offers important guidance about its use in other potential conflicts.