Well, south Canada and north Mexico at least are both part of Panem, it's not like the US alone turned into Panem. But yeah, I wonder about the other continents too. Whatever happened to destroy North America had to have impacted the rest of the world, too, right?
SPOILERS FOR THE BALLAD OF SONGBIRDS AND SNAKES:
The thing that's fascinating me the most right now is the difference between the way Tigris and Snow turned out. Reading the original trilogy, I never in a thousand years would have guessed that they were related, much less were as close as they were. It's a very interesting study to think about their personalities and the different choices they made over their lives, and why they made those choices. I think back to Tigris first only passively helping Katniss and the others when they came to her shop by allowing them to hide in her basement, but then when Katniss offered her the can of salmon as a thank you for helping them (perhaps triggering the memory of Tigris, Coryo, and Grandma'am's "feast" of salmon and turkey) it was like a switch was flipped and Tigris decided to actively help them by redoing their makeup, giving them Capitol clothes, hiding their weapons, etc. There's a lot to unpack there when you really start to think it through.