In light of the London violence, Kevin Kosar (a frequent Weekly Standard contributor) reminds us of the late political scientist Edward Banfield's sly--and revealing--comment on urban riots.  It's not a lack of government spending, discrimination, poverty, etc.  Often young men riot because it's fun to do:

Often, though, people riot "mainly for fun and profit," as Banfield put it in The Unheavenly City. Riots, as he reminded us, have been around as long as there have been cities. "In Pittsburgh in 1809 an editor proposed satirically that the city establish a 'conflagration fund' from which to buy twelve houses, one to be burned each month in civil celebration."

Kosar concludes, "[O]ne sure accelerant to riots present and future, Banfield explained, is the widespread belief that one can get away with it."  RTWT for clear thinking and illuminating links.  Kosar's website, covering higher education, reviews, Banfieldiana, and whiskey, can be found  here.