The defeat of Nazi Germany, the American Civil War brought an end to slavery in the US, the stemming of Ottoman power encroaching into Europe in the Ottoman-Habsburg Wars let Western Europe survive.
War is, by nature, destructive. However, there is, at times, good that comes from the waging of it. Evil things (I am not saying that hair colors other than ginger are evil. I am reffering to true evils) ought to be destroyed, and if war is the only way to do that, war must then be waged.