For most of history, war has been a more or less functional institution, providing benefits for those societies that were good at it, although the cost in money, in lives, and in suffering was always significant. Only in the past century have large numbers of people begun to question the basic assumption of civilized societies that war is inevitable and often useful.
As a man develops, he places a greater value upon his own rights. Liberty becomes a grander and diviner thing. As he values his own rights he begins to value the rights of others. And when all men give to all others all the rights they claim for themselves, this world will be civilized.