Negotiating a peaceful end to civil wars, which often includes an attempt to bring together former rival military or insurgent factions into a new national army, has been a frequent goal of conflict resolution practitioners since the Cold War. In practice, however, very little is known about what works, and what doesn't work, in bringing together former opponents to build a lasting peace. Contributors to this volume assess why some civil wars result in successful military integration while others dissolve into further strife, factionalism, and even renewed civil war. Eleven cases are studied in detail-Sudan, Zimbabwe, Lebanon, Rwanda, the Philippines, South Africa, Mozambique, Bosnia-Herzegovina, Sierra Leone, Democratic Republic of the Congo, and Burundi-while other chapters compare military integration with corporate mergers and discuss some of the hidden costs and risks of merging military forces. New Armies from Old fills a serious gap in our understanding of civil wars, their possible resolution, and how to promote lasting peace, and will be of interest to scholars and students of conflict resolution, international affairs, and peace and security studies.