for those of you who do not play fallout 3, the enclave was a shadow group inside the U.S Government before the great war of 2077 which ended the world, after the war, the enclave waited and then they came out of their bunkers and locations, intent on wiping out the mutants of the wasteland and rebuilding America
now the games have always made them the villian, well I dont see them in such way, although they did kill your dad in fallout 3 (( SPOILER, sorry )) I believe in their goal, and support the enclave 100%
this is just being posted as I am writing a fic ((along with RP War II )) about the enclave moving to the commonwealth to take over
Technically it's all the games. They were powerful on the west coast, got destroyed/ scattered there: which made the remnants in NV. All those who survived went to Chicago area or the east coast: where they were destroyed again.
the goal of the Enclave is the best course for the Wasteland, its just people rather be harassed by mercenaries, raped and pillaged by raiders and be dragged off by super mutants and slavers rather than being under the banner of a actual government that could have gripped the entire American Wasteland without a struggle.