One possibility could be that the richer cities were part of richer provinces that in turn allowed soldiers a higher wage and opportunities to remain professional. Poorer cities may not have been able to do so. I'd be interested in knowing what any studies on this have revealed. I think that the urban degeneration argument is only one possibility; the decline may be due to a multiplicity of factors and their interactions. To be fair, Conrad, you do suggest as much in your opening post.

I have other questions that I want answered, but I don't want to threadhog. I can ask them later.