The New Manhattan government cripples, and the Generals are assassinated. It is complete chaos around the city, no one maintains the streets any longer and the capital building has fallen, literally, crushing millions of citizens and government buildings and homes. Soldiers try to keep the peace but at this point it is a lost cause. Living in houses is too dangerous, and civilians are forced to live in the streets, their homes now makeshift lean-to's next to barrels of fire. Bandits roam the streets, which are now overrun by vegetation. There are the few, however, who remain underground, in the massive facility that spans under the entire city and then some. They wish for only peace, but are forced to shoot anyone that enters their dwelling. Men with stealth suits constantly patrol the outside, firing on anyone who looks remotely harmful, be it a man, a woman, or a child.
So yeah. Don't try to control the city or you'll get forgeted up. However, if you manage to make it underground, the bounty is endless. It's basically a "Vault" situation from Borderlands. Peoples around the city tell legends of countless treasures underneath the city, including weapons, money, and lost technologies.