Boros: Red/White soldiers, fanatic zealots who bring law and order to the streets, also a police force sometimes.
Selesneya: A White/Green hippy commune who believe in togetherness with their own army.
Golgari: Literal sewer people, Black/Green; they are people who deal with death and waste by recycling what people in the city throw away. They are also necromancers which helps them deal with the garbage.
Gruul: Big Red/Green smash punks who love nature before the city got built on top of it and tear down the city to bring nature back.
Rakdos: A Red/Black cult that worships a chaos demon by putting on a circus act for him; the circus act is highly sadistic and violent.
Dimir: Blue/Black secret agents who know everything. Their public front is as a courier and library service, though.
Izzet: Red/Blue mad inventors who love explosions and lightening.
Azorious: Blue/White. They love the law and maintaining the law. Law law law law.
Orzhov: A White/Black church that is also a bank. They literally put your soul in debt to them. Literally your soul. When you die your ghost has to work for them until your debt is paid off. Your debt is never paid off.
Simic: Blue/Green, they're also scientists but with animal abuse. They love to "self-improve" by mixing themselves with animal DNA as well as mixing other animal DNA. Sometimes accidentally or on purpose create giant kaijus.