Aaron Sandel, the codirector of the Ngogo Chimpanzee Project in Uganda's Kibale National Park, witnessed a rare occurrence of a chimpanzee "civil war" in June 2015, when he noticed a group of apes suddenly fell silent and began acting differently. The once close-knit community, known as the Western and Central chimps, began treating each other like strangers. Since that day, the violence between the two groups has grown, resulting in lethal attacks on adults and infants several times a year. The findings provide a unique glimpse into how shifting social ties can cause strife among nonhuman groups of animals.