Law enforcement officials estimate that tens of thousands of gangs are active across the United States, ranging from neighborhood street gangs to prison gangs and large organized criminal networks.

Anyone who has followed the devastating violence in California’s prisons knows that gang rivalries trigger a lot of the bloodshed. So it stood to reason that if the authorities could get members to ...

A system designed to protect state inmates has led to increased violence involving so-called ‘dropout’ gangs of prisoners who have defected from other groups. Authorities say one group, the Riders, ...