Where It All Goes Down
Korea—A Small Seaside Village, Sometime in the 1980s
Korea is like ground zero in this book: it's where everything begins for Young Ju. It's the place that provides a template for what she thinks a home should be like ("small… that sits like a hen on her nest" (4.22)), what language should sound like (not at all like English), and what family is (as far as she's concerned, it includes Halmoni at home).
Korea is also, by the way, where we get to see the beginnings of the chaotic family dynamics that shape the rest of the book, the dynamics that make Young Ju's little hen-like Korean home seem far from ideal. It's where she learns how to hide with her Halmoni and Uhmma from her Apa "[b]ecause when Apa is too quiet with the squinty eye, it is better to hide until he falls asleep or else there will be breaking everywhere" (2.4).
America—The Greater Los Angeles Area, 1980s-2000s
America is the opposite of Korea, with "many jobs, big houses, good schools" (7.35). At least, that's what it seems like at first, which is why Young Ju keeps thinking it's literally heaven.
But America is also where Young Ju's (and Apa's and Uhmma's) dreams go to die. This sounds really harsh, but it's only because these dreams are completely materialistic and depend on the Parks becoming impossibly wealthy… Which of course doesn't happen for Apa, who has to work two dead-end jobs, and Uhmma, who has to work at the back of a restaurant in order for the Parks to survive in the ghetto they move to.
However, what Young Ju and Uhmma (not so much Apa, unfortunately) gain are some serious life lessons, like how to work (really) hard and how to be brave. Could they have learned all of that in Korea?
Maybe… but it's only in America that Young Ju and Uhmma really learn how to stand up against Apa and be self-sufficient without a father in the house. And that's something that the book, at least, suggests would not have happened in Korea, where Apa really does rule the house. (Remember—even Halmoni hides in her own house when Apa gets angry.)