The vast majority of government-caused deaths take place during peacetime, not during wars. Prof. R. J. Rummel of the University of Hawaii estimates the ratio of those killed by governments in peacetime to those killed in wars at six to one. You can read more at his website:
http://www.hawaii.edu/powerkills/welcome.html
If the goal is to reduce the number of unnecessary deaths, it looks far more promising to replace authoritarian regimes with democracies than to tilt at the windmill of ending war.
Good point. I also would like to note that religion has NOT caused the most deaths in world history, unless one regards socialism as a religion. 100 million deaths at the hands of socialism madmen.