Augustine of Hippo
Just war

Augustine asserted Christians should be pacifists as a personal, philosophical stance. However, peacefulness in the face of a grave wrong that could only be stopped by violence would be a sin. Defence of one's self or others could be a necessity, especially when authorized by a legitimate authority. While not breaking down the conditions necessary for war to be just, Augustine coined the phrase in his work The City of God. In essence, the pursuit of peace must include the option of fighting for its long-term preservation. Such a war could not be pre-emptive, but defensive, to restore peace. Thomas Aquinas, centuries later, used the authority of Augustine's arguments in an attempt to define the conditions under which a war could be just.
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