Quite a lot, actually.
Writing recently in National Review Online, Jonah Goldberg asks, "War: What Is It Good For?" He answers his question, he closes his article by pointing out the morality of his position: "The biggest favor the United States ever did to militaristic Japan was to crush it militarily. Our victory ushered in prosperity, democracy, and a productive peace. The Iraqi people would be lucky if we did them the same favor."
Material progress is not the only boon of war. Society is often the beneficiary of battle as well. Democracy was born in Athens in the 6th century thanks to the Cleisthenean reforms, which were themselves the product of drastic military reforms. The rise of the infantry during the Middle Ages has been credited with sowing the seeds of democracy in the modern era. And even more recently, wars freed slaves here at home and abroad. Women's suffrage would not have been possible without war.
The idea that wars are never forces for good is the geopolitical equivalent of the old canard that violence never solves anything. The slaves freed by the force of arms certainly thought violence solved the problem of human bondage on American soil. The residents of Dachau no doubt saw some utility to war when American GIs opened the gates. War can be horrible and cruel, but it can also be just and morally necessary.
These examples, most of which come from Robert Nisbet's indispensable (though out-of-print) book Prejudices, are small illustrations of the fact that wars are not all bad. [More]
He makes a strong argument that is difficult to refute. looking at it from an historical perspective there is plenty of evidence to support these assertions.