In a series of recent articles, civil conflict researchers Esteban, Mayoral, and Ray (see this paper for an example) have tried to answer that question. Is it economic inequality, or cultural differences? Or maybe there is a political cause at its root. I encourage you to read the paper and to have a look at the video below. Here are a couple of images from the linked paper, which you’ll see remind you of concepts that we’ve covered in IS210 this semester. The first image is only part of the “Model of Civil Conflict.” Take a look at the paper if you want to see the “punchline.”
Here is the relationship between fractionalization and polarization. What does each of these measures of diversity measure?
And here’s a nice youtube video wherein the authors explain their theory.