I started reading When Jesus Became God the other day. It strikes me as the story begins that, while the details differ, people change very little over time. We tend to kill each other over faith, over quibbles about the nature of our god. Yet those quibbles change over time, as one warring tribe wins over another.
These semantic differences are enough to set tribes apart. And tribes, set apart, attack the Other.
We also kill over the color of our sox.