Data Modeling: ethnicities with parent-child relationship?

Well there is such a thing as an Ethnicity Group in the real world, so you do need two tables, not one. The real world has three levels (the top-most would be Race), but I understand that may not be necessary here. If you squash the three levels into two, you have to be careful, and lay them all out properly at the beginning.

However, they will be vulnerable to people saying they want the real thing, and you may have to change it, or change the structure to fit more in ... much more work later).

If there is nothing like an "ethnicity group" in the real world, I'd suggest you don't introduce one in your data model.

I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.