Lincoln is from Illinois—at least according to people from Illinois—so it's strange to find out that he was born in Kentucky, spent some time in Indiana, travelled up and down the Mississippi River as far as New Orleans, disliked Washington, D.C., spent a vampire-filled vacation in New York City, and, after he died and was turned into a vampire, spent more time fighting vampires in the South and eventually in Europe. Somewhere in there, he spent some time in the Land of Lincoln.
Except for that one line about Lincoln going to Europe, all of Lincoln's life and almost all of this book takes place in America the Beautiful. Poe spends some time in England as a student, Henry mentions that the Roanoke colonists came from England, and Poe describes Hungarian vampires. But other than that it's all America all the time.
But that doesn't mean that Grahame-Smith can just describe the setting by saying, "go, look outside your door—now imagine vampires there." Abraham Lincoln: Vampire Hunter may take place all over America (well, all over the East and Central areas—no love for California), but it's all over the 19th century, which is not right outside your door. (Unless it is—go look now.)
That means Grahame-Smith has to spend a certain amount of time slipping us some facts and history. And he very often does that by telling us some fun little story or by connecting the history to the important characters.
For instance, Chapter One includes all sorts of information about young America, which was growing fast and full of crime. To get this idea across, Grahame-Smith tells "a story of an elderly widow named Agnes Pendel Brown, who lived with her longtime butler (nearly as old as she, and deaf as a stone)" (1.15). That story ends with them being robbed totally while they sleep, which tells us how bad crime is and how deeply these two sleep.
That small story gives us the lowdown on 19th Century America: there's crime and no C.S.I. teams going around solving them. Which helps explain how Abe gets away with just killing vampires—no one is dusting for his fingerprints or tracking him with spy satellites. Boo.
Look for more stories like this as you read.
For another example, we hear that Abe loses his younger brother Thomas Jr. after only a month. You might suspect vampires (who do a great deal of killing in this book), but as it turns out, kids just died a lot back then.
As the narrator notes, "It's impossible to know what killed Thomas Lincoln Jr. […] Even under the best conditions, the infant mortality rate was 10 percent in the early 1800s" (1.31). That's an example of how the narrator sneaks in a little info about this setting by connecting it to the characters and their lives (especially Abe's family). Thanks, buddy!
Can you imagine a version of this book where Abe Lincoln is a world-traveling vampire hunter? Well, no, because Seth Grahame-Smith is mostly trying to stick to the real history and without a jet (or jet-pack), traveling around the world would just take up too much time.
Okay, but we could still get glimpses of what's going on with the rest of the world. Like when Seward travels to Europe (10.48) or when Henry has his vampire spies and contacts in Europe (12.17), the narrator could tell us all about that. Why don't we hear about that? Is it just because the narrator wants to keep the focus on Lincoln?
That's probably one reason, but we also think the narrator keeps the focus on America because this book is largely about masters/kings and their slaves. See, in the middle of the 19th century, the United States was almost the only democracy in the world. (Europe had lots of revolutions in 1848, but they didn't really succeed; by 1860, most of Europe still had kings and queens, though there were also some parliaments and congresses floating around [source].)
As Abe Lincoln says, this is one reason why he hates slavery: America is the only democracy in the world that says that people are created equal, but slavery makes the Americans seem like hypocrites. As Abe says, "'I hate [slavery] because it deprives our republican example of its just influence in the world! […] Enables the enemies of free institutions, with plausibility, to taunt us as hypocrites!'" (9.31).
In the end, it's really quite simple. The narrator keeps the focus on America because this is an American story. It's the story of a famous American character (Honest Abe) fighting for the principles of America (equality, anyone?) that have been messed up by, well, other Americans (and their vampire buddies).