After years of decline, homicide and gun violence are surging in U.S. cities, and many law enforcement officials say street gangs are a major reason for the increase. Gang membership has soared in recent years, and crimes committed by gangs have expanded beyond drug dealing and murder to migrant smuggling, sex trafficking and counterfeiting. Gang leaders are using the Internet and social media to communicate, recruit members and threaten rival groups. Meanwhile, gangs are spreading to smaller cities, suburbs and even rural areas. Legal injunctions — restraining orders that bar gang members from congregating publicly — have curbed criminal activity in some localities, but critics say the tactic violates civil liberties, is applied in a racially biased manner and unfairly stigmatizes innocent young people. Countering the gang threat requires a multipronged strategy, many experts say, that combines tough policing with anti-poverty programs that seek to keep youths from falling into the gang lifestyle.