@Kommando_J: I freely admit that my knowledge of world events during the 1800s is pretty limited beyond the Civil War and the 'Old West'- but there's nothing to stop you taking the DA alternative history wherever you like- in fact, I'd love to see what you come up with (and I always welcome learning more about a period)! Here are a few starting points:
1) There are still vampires in the rest of the world- perhaps old rivals or servants of Dracula, and the outcast Severed Clans. Now he's 'busy' in America, they will be expanding their own interests!
Meanwhile, the misguided human members of the Cult of Lilith continue their long, worldwide search for the Spear of Destiny, said to have once been wielded by the Mother of Vampires herself.
2) Likewise, there are still chapters of the Twilight Order based in the Old World. They have an uneasy alliance with the Vatican, and indeed have often been forced to work more closely with the Pope's so-called 'Helsing Agency'- officially sanctioned supernatural investigators and priestly monster-hunters, named after an ancestor of our good friend Abraham.
3) The Eldritch Incursion and Plague of Madness did not only affect America... Various Mythos cults have resurfaced, and the remnants of the old Sisterhood bloodlines still in Europe have begun to awaken in response.
@Paboook: Keep your eyes peeled, my friend- all being well, rules for an urban setting will be on their way in the future... While not directly themed to Fortress Washington itself, hopefully you will find some stuff of interest!