Simurgh. Youngest of the Endbringers. Smallest. Least destructive. The 'little sister'. If you believe that, you're too stupid to live. She's the cruelest of the three. Her "brothers", at least, are quick about it. Death is a mercy Simurgh offers sparingly.
Oh, sure, she doesn't do what her "brothers" do. Behemoth will turn a city into a radioactive hell. Leviathan will sink that same city into the ocean. Or leave it broken by waves and filled with stagnant water and all the disease that comes with it. Not Simurgh. She is more subtle.
She leaves her poison inside people. Her Song. Every living being that's been exposed to her for more than a couple hours is 'infected'. A twisted combination of telepathic manipulation and the ability to sense the future. After you've been exposed, you're a weapon. A bomb. Set to self destruct. A day. A month. A decade. Sooner or later. And there's no way of knowing just what she did inside you. What sick plan was set in motion the moment she sank her claws into your mind. Destroyed your future. Made you a tool in her plan.
And then she appeared over Washington DC. Evacuation procedures managed to evacuate much of the area. But not nearly enough. Nothing is ever enough. The (former) President was caught, along with a number of others. They didn't even let him out of the quarantine to effect his resignation.
And that's what they're calling it. Quarantine. We're infected. Whether we were bigwig politicos, or just bums who were living in the streets before the attack. It doesn't matter. We're too dangerous to let leave. They made it clear that anyone trying to escape would be shot.
The pentagon burned within minutes after the attack ended. The walls were assembled before an hour had passed. Food gets sent in by robot AI.
The Protectorate, PRT, police and military that were unfortunate enough to be caught within the walls still have their jobs- though, now, it's to maintain what semblance of civilization they can. While the shock lifts, and what all this means slowly starts to set in in.