riots are a mingle of things, also to be pointed out, the sheer numbers of immigrants on european countries have increased exponentially.
Now, from a cultural point , immigrants wont relate to the country that harbored them, and lost links with the one they came from, feel a void.
religion, as said, france keeps a strict division of state and religion,
and some communities segregate themselfs in the process, and feel harassed in several ways, and the government has a bad tendancy to say "keep me out of it", when they should be active and combat seclusion.
and economics, as european economies are in the dump, people keep forgetting that the time when the state was everybody's daddy has ended. The poor and the immigrants are always the first to suffer from the cutbacks. Socialism has it's costs.
blame to go around, specially after 9/11, for the economies and harassment of muslims.
but Oliver Stone's Conspiracy Theory? Sorry.
lets not turn this into a "lets bash the french" type thread.
too many on fark.
PS: there is an increasing tension between local populations and immigrants as the locals feel as they are being cheated of "their" jobs by them, specially now, as unemployment runs high. Funny as them, immigrants, fill a need for labor, specially for jobs that the "locals" arent interested in performing (like trashmen, oops, sanitation engs.

). Sometimes not even about money, but some foolish pride.