About 1,000,000 for a medium scale war like in Afghanistan. But world wars? PFFT About 10~15 million.
Op, are you serious? It depends completely on intel you have; wars are won with brains more than they are with brute force (although it obviously helps a considerable amount to have both).
"AllThough it matters who's got a bigger stick it matters a hell of a lot more who's swinging it." general Shepard mmw2