|Servant of God, Dorothy Day|
Since the time that Jesus spoke with an other-worldly authority, Christians have been forced to grapple with his radical non-violence: “I say to you, love your enemies, and pray for those who persecute you” (Mt 5:44); “Put your sword back into its sheath, for all who take the sword will perish by the sword” (Mt 26:52). Jesus was not naïve: He personally felt the violence of an unjust and fallen world. And yet he made no easy compromises about using worldly power or resorting to violence.
Christians of the first centuries saw military service as incompatible with walking the path of Christian discipleship--not because they were unwilling to die in service to the empire, but because they were unwilling to kill for it. From the time of St. Augustine on, however, the Church realized the necessary role of the state in protecting its citizens from aggressors, and Christians were allowed to help provide military defense of their fellow citizens. Thus a theory of “just war” principles emerged, in an attempt to provide moral guidance to individuals and nations regarding how best to promote peace. The theory was guided by the assumption that defending oneself and one's people from an aggressor is qualitatively different from being the aggressor, or from resorting to “pre-emptive” military strikes or "preventative warfare."
In a powerful section entitled “Safeguarding Peace,” the Catechism of the Catholic Church discusses war within the context of the fifth commandment’s prohibition of killing (CCC, 2302-17). Two passages that seem particularly noteworthy today: