So, in my writing, the Point of Divergence was at the very beginning of Sherman's March to Atlanta. That still turned out the same, maybe even a little faster due to the events that happened. In my world, Vampires, and shapeshifters, maybe even magic has always existed. It was kind of hidden, but it was there. it was real. For America, that was an old world problem. Something for Europe and the rest of the world to deal with. that particular plague hadn't spread to North America. Or so they thought.
Burning down the wrong plantation in northern Georgia dissuaded them of that notion rather quickly. It ended up with vampires and the like having a quasi independent legal status in a series of Preserve's throughout the country. So now, you have vampires living out in the open in the United States. How is that going to change how internal American history progresses. Does the westward expansion get slowed because suddenly the Cheyenne Dog Soldiers turn out to be more than just a really cool and intimidating name?
Certain events will still have to happen. If for no other reason than to give a sense of the familiar to anyone reading the stories. And some things have enough momentum behind them that even the presence of werewolves isn't going to stop them from happening. They may just be changed a little. Native Americans may still end up on reservations, but if they had shapeshifters in their population it may have taken a lot longer, and in a lot of cases ended up with a stronger bargaining position. In my world, they're still there, they're just a lot more independent and stronger than they historically were. A treaty is less likely to be violated when one side has people who can turn into giant wolves or bears, etc.
I like starting off relatively small. I focus on the United States and how the country reacted to supernaturals first. The creation of the Department of Supernatural Affairs (with a little blending them with Pinkerton Detective Agency style work after the Civil War). Various anti supernatural laws where certain places a shapeshifter is gonna be shot on sight no questions asked. Innocent or not. And it's not just how the government is going to react, its how the people are going to react. Some people won't really mind a new group of people in society, but history tells us that's not going to be the general opinion. Suddenly segregation and all that went along with it get's added to an entirely new group of people.
Some people, especially in modern times, are going to build an overly romanticized mythos around these creatures. Whether that image is true or not gives good writing opportunities. But look at it this way, look at how popular media portrays vampires in the real world. There's always this element of sex and seduction mixed in with the horror and the violence. In my mind, vampires are going to play off that. It makes their lives easier if the general public views them as quasi celebrities and sex symbols. Hell, the Preserves are tourist attractions. Come on in, see and experience the creatures of the night up close and personal. Just be sure not to look to hard at everything else that goes on. Sex sells, and vampires are fully willing to take advantage of that. If your food comes to you, willingly, you don't have to sneak around the shadows anymore. Well, unless you want to.
Though they're going to make damn sure their adoring fans don't know what really goes on. Bad for business.
So in the United States, the vampires and shapeshifters, constrained as they might be, are going to flourish and thrive.There is likely going to be a hell of a lot more of them in one North American city than there is in all of Europe where they don't have the advantage of being out in the open and not having a stake driven through them at first sight.
A larger population makes them more powerful, and more dangerous.
Will write more on this later, but for now, its a good start.