Yeah, there'd be war.  I think most "religious" wars have non-religious causes like ethnic hatred, land disputes, power, and politics.  I mean take a look at the world's major religions; they all preach peace and harmony.  It's the people themselves who distort the religion to fit their own needs.  If it weren't religion, it'd just be some other unifying factor such as race, nationality or ethnicity.  War is caused by something in human nature, not in religion.