Racism. Since race as a collection of physical traits is not really a scientific concept, it's difficult to distinguish between purely racial conflicts and all your other garden-variety ethnic conflicts. Whether a conflict is racist or not seems to depend entirely on whether the enemy originated just across the mountains or half a world away. Generally, what people mean by racism is probably covered by African Diaspora, Apartheid, Colonial Activities and Indians.
Generally speaking, in most of the following cases, religion is both the stated cause of the killing and the only substantive difference between the two opposing groups. Obviously, there would be many additional conflicts where religion is just one of several divisions.