Drug traffickers sometimes divide profits via peaceful agreement. Other times they fight. We propose a model to investigate this variation, focusing on the state’s effort to enforce prohibition. Seizing illegal goods generally increases trafficker profits, and higher profits fuel violence. Killing kingpins makes crime bosses short-sighted, further hindering peaceful pacts. The results help explain empirical patterns of violence in criminal war, which is less studied than interstate or civil war but often as deadly.