Yes that is true also.Nationalism can promote hate or fear, I feel its an outdated concept used to divide humanity as a whole.
But governments use this all the time.
Here is an example.
Most people think killing some one is wrong. But yet when your country goes to war, for what ever reason. Then people think that killing some one is a good thing. To the point that even in the country that is a war, the citizens in that country that don't want to go, are considered traitors. And maybe imprisoned.
So people will hate even ones from their own country because of their stand.
Then governments also will make hero's out of ones that have done a good job of killing others. This is a total lack of getting the world together.
So it is not just religion, there are many other situations also. For some it is just the want of power. For others it maybe a lure of natural resources of another country. Sometime is just because of pride.