Mortgage foreclosure rates for US single family homes are expected to range between 10-15% over the next three years -- with some neighborhoods well over 30% (for example: in the San Diego exurb Temecula 15% of homes are already either bank-owned or in some stage of foreclosure). The Chicago Fed has found that under normal circumstances, every increase in the foreclosure rate by 2.87%, there is a 6.68% increase in violent crime. Further, housing values fall by nearly 1% for each foreclosed home within 1/8 of a mile.
The Swiss Cheese Effect
As US cities, suburbs and neighborhoods begin to look like swiss cheese, there's little doubt that the US will experience a radical increase in the formation of gangs, militias, and other violent groups. A volatile mixture of wealth/expectation destruction, neighborhood decay (due to empty and abandoned properties), and a visceral sense of economic betrayal/abandonment will be the drivers. Connectivity (both local and global) will ensure that the damage spreads virally.