Don't just gloss this one over. After all, the setting is basically the most important aspect of Moon Over Manifest. How do we know?
(1) It's historical fiction. (Check out "Genre" for more.) That means history (a.k.a. setting) is a Big Deal.
(2) The name of the setting is right in the title: Manifest.
The whole stinkin' story revolves around Manifest.
But it's even more complicated than that. Manifest has a much deeper meaning than just being the place where everything happens. It represents hope, home, community, pain, and loss for all its townspeople. The town sign used to say: "MANIFEST: A TOWN WITH A RICH PAST AND A BRIGHT FUTURE" (1.1), but it's been shot up so much that now it only says: "MANIFEST: A TOWN WITH A PAST" (1.10). And it takes two outsiders to the town—Jinx and Abilene—to bring the townspeople there together as a community.
Why weren't they a community to begin with? Well, 1918 Manifest was a town of immigrants, and everyone had a different background and a different language. They needed a common cause to bring them closer—and Jinx helped with that. When Abilene gets there 20 years later, they need something different: in order to heal the divisions in the community, they need the truth of their past to be revealed.
I looks like Sister was right to have Abilene look "manifest" up in the dictionary: "a list of passengers on a ship" (26.78) and "to reveal, to make known" (26.80). The town name says it all, and the setting really determines this whole story.
Let's not forget the tiny matter of what's going on during the two historical time periods in which our fictional stories are set. (See the "Genre" section for even more on that.)
(1) 1918. Hmmm, let us think. What was going on then? Oh, ever heard of a little spat known as World War I? Pretty important for our story, too, since Ned goes off to fight, and a big chunk of the rest of Jinx's life is affected by Ned's death at war.
(2) In 1936, the Great Depression was still in full swing. People were struggling to survive, and at the same time members of the KKK (whom we see in the book) were making things even worse in the years leading up to World War II.
Needless to say, we're in two majorly important eras right here. So while we focus in on little Manifest, Kansas, we can't forget that the rest of the world was spinning right alongside it.