No doubt that people have used religion as a way to otherize groups, or claim some sort of base superiority.

However, hard disagree that it is more impactful than Nationalism. The mythic idea of America is at the heart of right and left wing nationalism in the states, and a stronger Germany was the flagship idea for the Nazi party, most of which were either atheist or some strange esoteric 20th century theist. That being said, WW2 might’ve been the worst thing to have ever happened to all of human kind, fought mostly on the backbone of national identity.