Just war
From PhiloWiki
In 410 A.D., barbarians, discontent that they lacked full Roman enfranchisement, sacked Rome. The pagans blamed the Christians for this defeat on the grounds that Christian doctrine renounced the political and military necessities of this world.
Although the Empire was already Christian by this point and Christian soldiers proudly fought on the frontiers, the pagan criticism acquired some currency. Addressing these accusations, St. Augustine responded that Christians were not to blame and, laying the foundation for later just-war theory, argued that in a good state there are circumstances for the defense of one’s country. Barbarians, after all, lived on the borders and were intermittently invading, and a military presence is all that could protect Roman cities from political and moral chaos.
