What Is Ego?

All the religious conflicts that have ever occurred in history have all been the result of ego. How about cast systems and power hierarchies, for example, like the indian cast system? Where does that come from? Ego. The oppression of human rights and civil liberties? Throughout pretty much all history, what has been the source and the motivation for that? It's been ego. All the problems we have with government with war is this kind of stuff, it really isn't any different from what happens with the destruction of the environment.