Once an urban problem, street gangs have now infiltrated U.S. communities large and small. Gang experts say at least 21,500 gangs — with more than 731,000 members — are active nationwide. Long-established domestic gangs like the Bloods and the Crips remain powerful, but the problem has worsened dramatically in recent years. Heavy immigration, particularly from Latin America and Asia, has introduced highly violent gangs like Mara Salvatrucha and the Almighty Latin Kings Nation. Bound by tight ethnic and racial ties, they often stymie police investigations by assaulting or killing potential witnesses. Having already diversified from illegal drugs into auto theft, extortion, property crimes and home invasion, some East Coast gangs have begun trafficking in fraudulent identification papers that could be used by terrorists. While experts agree gangs are more pervasive than ever, few agree on a remedy. Proposed legislation would increase penalties for gang membership and gang crimes, but critics say it won't solve the problem.