MS-13 is now the biggest street gang, reportedly, with 6 - 10,000 members in 46 states, according to the FBI.
The origins of the gang is refugees from conflict zones like El Salvador (the name "Mara Salvatrucha" comes from the peasant fighters in the civil war there). The Latin refugees opposed Black and Mexican gangs in LA initially, and then spread to Latino communities across the U.S. The biggest cluster of members in in Suffolk County, Long Island (over 400 members), according to the NY Post.
MS-13 has made news headlines lately for violent killings.
According to Guardian Angels (a non-profit international volunteer organization of unarmed crime-prevention patrollers) founder Curtis Sliwa, “MS-13 is unlike any street gang that we have dealt with before. They are organized and behave like a paramilitary organization. And the violence is incredibly brutal.”