I remember a 60 minutes expose about MS13 from better than 20 years ago. It was a long time ago but I’m pretty sure MS13 started as El Salvadoran guerrilla fighters. When the war ended, they turned to extortion, murder and terror.
They did things like stopping a bus on a country road and killing all but one person to take a message to the surrounding villages that MS13 was in control.
I don’t know much about the Mexican ‘mara’ gang either. Or even if the Judas Priest reference is correct! El Salvadorian metal heads? whod’a thunk?