In 1990, shotguns and M-16s were adopted into Enga warfare, setting off some 15 years of devastation as youths (~17 to 28) took charge of interclan warfare. In response, people called on elder leaders to adapt customary institutions to restore peace; subsequently, war deaths and the frequency of war declined radically. Data from precolonial warfare, 501 recent wars, and 129 customary court sess...