It is, to large degree, the tragic outcome of dysfunctional tax, educational, and regulatory policy. Newt Gingrich gave an interesting speech on the fall of Detroit last year:
I'm not sure exactly what you mean by a "large degree," but the story of Detroit is more about race than it is about any of those things. (It's also about the auto industry, of course, and poor government.. but those are intertwined with racial issues as well.)
http://www.youtube.com/watch?v=oNM6HHJTUMM