The Mongols are a waterborne go-gang based in Los Angeles. Which is the 3rd oldest gang in North America (with the Latin Kings and Mexican Mafia being older), and formerly the oldest biker gang, being over 100 years old having been established in 1969 in the former United States (California).
The Mongols were originally a Latino-dominated traditional, old school biker gang. It has adapted to a flooded Los Angeles. Rather than motorcycles, they now use boats and juiced-up wave runners. They love to terrorize the few remaining inhabitants of the inner city, extorting cash and stealing what little they have. Small corporations' rebuilding efforts experience problems caused by the Mongols but they leave the major corporations alone.
The Mongols historically had a relationship with the Mexican Mafia and more recently various "Sureno" gangs, therefore it is possible that it is either still aligned with the Mexican Mafia or it has a business relationship with the prison gang.
In the real world, the Mongols biker gang has been around since after the Vietnam War. It's a brutal and ruthless "One-Percenter" motorcycle club similar to other such gangs (Hell's Angels, Outlaws, Pagans, Bandidos, Warlocks, Vagos, etc) which are involved in a variety of criminal activities, some of them being basically street gangs on Harley Davidsons and others (e.g. Hell's Angels) having evolved into organized crime.
The Mongols are of the latter type, based in Los Angeles. Deeply involved in the drug trade with a membership of hundreds in the United States and several hundred more worldwide. It's a biker gang with a membership that is mostly Latino in the United States, though elsewhere such as in Australia it's mostly Caucasian. They were allied with the Mexican Mafia, then the alliance fell apart and war erupted between the two, and now there is peace again between the two with the Mongols reported to having agreed to take action to fix the reason for the conflict.
- Corporate Enclaves p.52