Daniel Pipes has an item on the rioting in Holland, which, while less serious than the WTC and Madrid, involved more Muslims.
Enough to make it a full-on civil war type situation, kind of like the Watts Riot. He writes:
There have been larger Islamist attacks in the West – such as the two assaults on New York's World Trade Center and the Madrid train station bombings – but nothing has resembled the civil-war quality of the 15-hour standoff in The Hague, Holland, yesterday. [Weblog A Muslim Uprising in Holland? November 11, 2004]
This can happen here, you know. It might not be Muslims, who aren't concentrated enough, most places, in the United States, the way they are in Europe.
The point is that if you import millions of people from riot-prone areas, and cluster them in barrios, banlieues, or whatever, then rioting is more or less to be expected—unless the Administration starts enforcing the immigration laws.