Before Emperor Constantine instituted Christianity as the "national religion" of the Roman Empire in roughly 313 A.D., the majority of Christians' held a nonviolent stance. Many early church fathers interpreted the teachings of Jesus as advocating nonviolence. Several church fathers may be cited such as: Saint Maximilian, St. Martin of Tours, Athanasius, Cyprian, Clement of Alexandria, and another with the famous quote " Christ, in disarming Peter, disarmed every soldier."--Tertullian. After Constantine made Christianity the religion of the Empire, virtually requiring citizens to become a Christian or face execution, war and violence become much more accepted as a practice by Christians. How was this justified and how do Christians justify war today? Predominately the Just War Theory. This theory was supported by church fathers such as, Saints Augustine and Aquinas. The theory normally lists 7 principles or criteria for determining whether or not a war is just or not. If the war meets these criteria, it is pronounced "just" and permissible to initiate or be participated in by Christians.
The seven criteria generally go as follows: