Religion has historically united people but also caused conflict by dividing them into in-groups and out-groups. Over time, religions originally seen as unified have split into sects due to differing interpretations and political influences, fueling tensions. The document discusses how sectarianism arises from feelings of threatened religious identity and loyalty to one's own sect. It reviews literature analyzing the social and political dimensions of sectarianism historically within religions like Christianity, Islam, and African-American churches. Conflict theory is discussed as explaining how elites use religion to control the lower classes.