But background is ever so important. Alan Moore's Writing for Comics, written in the 80s before Watchmen became the gold standard of comic books, described world creation as the first element of a story, before plot and character, for the environment would lay down the rules and devices from which everything would follow. This is sound advice for writing fiction in any medium. Michael Chabon understands this (and The Amazing Adventures of Kavalier and Clay proved he knows a thing or two about comics to boot) and he must have had a merry time dropping the Jews into Alaska and seeing how their society and broader history would develop.
Take the ultra-orthodox Hasidic Jews. Something of a marginal group in our world (this much I gathered from a production of The Chosen I recently saw), in Chabon's Sitka, Alaska they comprise a robust criminal underworld. Our anti-hero, Detective Meyer Landsman, and his partner Berko need to speak with a Hasidic crime boss, and to get to him they go to the most powerful non-Hasid Jew in the Hasid territory of Verbov Island--Zimbalist the boundary maven, powerful for his mastery of intricacies of the Hasidic dogma of the eruv:
Landsman has put a lot of work into the avoidance of having to understand concepts like that of the eruv, but he knows that it's a typical Jewish ritual dodge, a scam run on God, that controlling motherfucker. It has something to do with pretending that telephone poles are doorposts, and that the wires are lintels. You can tie off an area using poles and strings and call it an eruv, then pretend ont he Sabbath that this eruv you've drawn--in the case of Zimbalist and his crew, it's pretty much the whole District--is your house. That way you can get around the Sabbath ban on carrying in a public place, and walk to shul with a couple of Alka-Seltzers in your pocket, and it isn't a sin. Given enough string and enough poles, and with a little creative use of existing walls, fences, cliffs, and rivers, you could tie a circle around pretty much any place and call it an eruv.
This isn't a heavy-handed plot device, but an element that arises naturally from the rich environment Chabon has created. We can conveniently gauge its being organic to the reality of the story by looking at a real-world example that ties in (oh ho!) nicely with this discussion:
The key to this kind of scene-setting is not to take it too far. For a whole world cannot be shown in one book, only the relevant sections. Chabon, though, as I wrote awhile back, is great at only supplying the reader with just enough information. He plays a balancing act of informing while acting as if it's all common knowledge anyway, leading to some great deadpan exposition:
In the corner by the door stands the famous Verbover Clock, a survivor of the old home back in Ukraine. Looted when Russia fell, then shipped back to Germany, it survived the dropping of the atomic bomb on Berlin in 1946 and all the confusions of the time that followed.
If anything the creation of an alternate history is more difficult than that of a whole new world, for its plausibility will always be weighed against that which actually happened. And this is just the setup on which a narrative will stand! I'm eager to see how it plays out.