Honestly, they could have and should have just made an all-new similar faction to serve the purpose they did in FO3. The Brotherhood of Steel as it was in the original games consisted of the descendants of soldiers deployed to the Mariposa Military Base to oversee West Tek's research on FEV before they took refuge in the Lost Hills bunker. There are plenty of other secure places in the US where military personnel and/or tech obsessives could have been stationed, especially in proximity of the DC region, which could easily have been one of the most militarized places in the world. Heck, the FO3 Brotherhood equivalent could easily have formed from the people overseeing the Liberty Prime project! We didn't need a chunk of the Brotherhood to have hiked all the way from one coast to the other for that purpose.

Honestly, they could have and should have just made an all-new similar faction to serve the purpose they did in FO3. The Brotherhood of Steel as it was in the original games consisted of the descendants of soldiers deployed to the Mariposa Military Base to oversee West Tek's research on FEV before they took refuge in the Lost Hills bunker. There are plenty of other secure places in the US where military personnel and/or tech obsessives could have been stationed, especially in proximity of the DC region, which could easily have been one of the most militarized places in the world. Heck, the FO3 Brotherhood equivalent could easily have formed from the people overseeing Liberty Prime! We didn't need a chunk of the Brotherhood to have hiked all the way from one coast to the other for that purpose.