The Enclave are the Antagonist from the Game Series Fallout.
The World has been destroyed by a Nuclear War, yet the Federal Government persists and demand the survivors loyalty. Even if it goes up against the New Societies Americans have created from themselves such as the New California Republic.
The Federal Government was just like a cockroach, even a Nuclear War couldn't kill it.
Also TEXOKIE, They were heavy on propaganda (broadcasts from roving robotic machines and via radio) and simply walked in and took what they wanted. Survivors were considered utterly expendable. In the game, the Enclave gave the remaining ‘Americans” (In quotes as America as an entity had ceased to be) a choice. cooperate or die. Anyone considered to be tainted by mutation was subject to immediate eradication.
There are many things about that game which I am convinced the developer hired experts to research...scenarios and such. While there is a considerable sci fi element, there are many very real scenarios and scientifically, psychologically and sociologically supportable truths to be found.
Thanks so much for the clarification!