We are a tribal animal. We're the descendants of tribal animals. We naturally divide our groups into "us" and "them." It's just the way we work, and I'm sad to say there's no way around it because the bottom line is that we are the products of biological processes that have favored tribalism since the late Pliocene, and fifty years of golly-goshing isn't going to sweep that away.
Especially when the golly-goshing is coming from people who are themselves riven with tribalism. Do you walk arm-in-arm with freepers? Nah, they're an "other." They're those people over there that aren't your people, and you avoid dealing with them. Do you walk up to strangers and treat them as if they were your sibling? probably not, because you don't know them - more tribalism. Do you identify by any ethnic group? Religious group? National identity?
Hell, here you are thumping your back about how superior you are, how high and elevated and magnificent you are compared to those people - not that you're even remotely close enough to their circumstances to make such a judgement. yet here you are. Secure in your smug self-assurance that you're just a better person overall. For all you know, if you were a Neur, living in south Sudan right now you might be in this group and you would likely feel you had a pretty fucking good reason to be there.
We're a tribal species. We define ourselves by groups. It's just the way we are. Ignoring that reality is just spinning your wheels in the sand, and outright denying that reality actually causes more problems.
It's especially imperative to understand this because of the direction we're headed right now. Energy crises are going to cause a decline of travel and communication, effectively making the world a larger place. At the same time, climate issues are going to spur human migrations - big ones. People will become more isolated, at the same time as disparate groups are butting over territory, provoking sharp distinctions of "us and them." If your interest is peace between peoples, it's necessary to realize that there even is such a "between." It's necessary to realize that for whatever reasons, people see each other as separate and often competing groups, and work within that framework for progressing.
Or you could keep telling the Dinka and Neur that there's no such thing as "Dinka" and "Neur" and see how far that gets you