D
Even if everyone is of the same race, people will always find differences that proclaim one subgroup superior or inferior to another based on things like religion, wealth, culture, or even abitrary matters. Shia and Sunni muslims are killing each other in the middle east. Hutus massacred thousands of Tutsi in the Rwandan genocide. Nazis murdered their Jewish minority. Native American tribes were in war with each other before the white man came along. Europeans engaged in constant conflicts for hundreds of years.
