The simplest, most respectful of personal freedom, way to wage war would be to conduct a poll of people willing to die for those declaring war upon one another, and then gather those people up and deliver them to the enemy to be summarily executed. When either side runs out of people willing to die for it, the war is over. Those willing to die get their wish, and all those that simply wish to live their lives without violence can then live without being "collateral damage". A win-win situation.