The point is, “they seem like nice enough guys” tells as jack about the future. By all accounts, South Sudanese are nice folks without any unappealing features. That wasn’t enough to make South Sudan work.
No, it never did. Not unless you take it all the way back to ancient Corduene, located in the heart of the Kurdish region along what is now the Turkey-Iraq border. Corduene was independent in the 2nd century BC, and was apparently named for the Kurds.
What makes a people a “people” is a complex matter - often, it is a case of self-identification; sometimes, it is pushed on a ‘people’ by outsiders.
Israel is a good example of that - the various persons who self-identify as “Israelis” these days have very little in common with each other before self-identifying as “Israeli”, even among the majority Jews - not language or race, certainly (they range from lilly-white Polish Ashkenazim, though Arabic looking Mizrai, to Black Bene Israel from Ethiopia).
Essentially, ethno-nationalism is fully capable of creating its own definitions of ethnicity - for good or bad.
The problem in the modern West is that we have become convinced that none of that applies to us - that we have created states that are truly above all of that, states that anyone, regardless, can join by an act of will. However, the immigrants to Western countries often find that, for various reasons, this is not true - that “neutrality” is simply defined as ‘accepting the majority culture in its totality’. Canada and the US are better in this respect than Europe, but still - it’s a spectrum I think, not a binary state. It is slightly disingenous of us in the West to absolutewly reject states simply because they are based on some form of ethno-nationalism. Better to see how they behave towards ethnic minorities in actual practice.