Uncle Ryze's background look like Bilgewater
Do you remember when I said that Death Blossom Kha'Zix's background looks like the Shadow Isles?
Well, Uncle Ryze's artwork looks like a Bilgewater setting, with the backgroung resembling a Bilgewater port or fort. Notice the Twisted Fate cards, as well as Katarina's blades (she has a Bilgewater-themed skin too)
I guess Riot decided to make this skin have more to do with the in-game universe instead of being just a skin based on the United State's supreme icon.