Are you saying war has been started by atheists in the name of atheism, or just that atheists themselves have started a war? I'm sure the second one may be true (although I don't know off the top of my head who they would be, undoubtedly there are historical atheists behind the start of a war; being an atheist doesn't immunize your from being a violent, psychopathic asshole.) Typically humans aren't going to respond passionately to negative identification, whereas positive identification typically is how one would inspire fanaticism, at least, passion.