200000 years ago more hominids died at the hands of hominids than anything else. There was no language. There was war. Now with language and technology there is the least of all reported war death. You are not doing it right.
Other elements can cause war; Famine, greed, difference in political ideals, radical patriotism (almost equivalent to religion), revenge, racial & ethnic prejudice, etc. Basically, irrational human behavior causes war in general.
Religion might not be the greatest historical reason for wars. Even without religion, we would still fight over resources. As the world gets smaller, resources like water, oil and rare-earth ores will become more and more contentious.
Sure would be wars, but warlords would need other stupid reasons to control the masses than religion. Religions over history were (and still are) giving this world reasons, if not excuses, for another war and another!
What's really annoying is that people would believe such nonsense and always have been driven and controlled by religious ((thoughts, icons, etc.)) to kill and to destroy.
It all comes with humanity's mind evolution,plus, the time would come to find there is no more religions, then the world would be a peaceful place.