Tribalism and nationalism are often mistaken for religion because different ethnicisities often have different religions. Example: during the "troubles" in Northern Ireland the flags flown by the two sides were not the banners of the Catholic Church and the protestant churches, but were the secular flags of Ireland and the U.K. It was a fight between the Irish and Scotch-Irish for domination and wealth in the north - nobody tried to convert anybody.
The main exception to my argument is Islam. Many muslims believe the Sharia requires that any "apostate," i.e. any muslim converting to another religion, be executed. Many madrassas teach that the meaning of "jihad" is the killing of non-muslims. I think nationalistic and economic reasons underly much of this, but the way many muslims speak of "jihad" and "martyrdom" is frightening.