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If war is a political instrument, then it stands to reason that the simulation of war can also be used to influence nations. While militaries have long conducted practice exercises, modern war games with their focus on strategy and counterstrategy, are only a few centuries old. The Americans began to use geographical maps to test potential war tactics in the late 1800s. And war games became part of the curriculum in military academies in 1894. In the 20th century, war became more complex. War games moved into the actual field, with the military conducting live exercises. Since World War two, the US has simulated hundreds of aerial and naval assaults. In today's war games, computer imitation do much of the heavy lifting. As commanders deploy in the field, programs calculate casualty rates. Computers adjust for weather factors and render a score, allowing the games to come as close to war as possible without imposing real violence.