Alright, I know it's simple and just using the 8k-bam, but here's an alternate America from 2100 map that's more interesting (in my opinion) than some kind of second american civil war.
By 2100 the US has endured many hardships blah blah blah climate refugees and 50 meters of sea level rise blah blah blah weakened federal government and tons of people start living off-world, assorted world governments begin a bit of an environmental reconstruction of the (what else) world.
The US has 6 (important for this map) breakaway states:
The Commonwealth of New England - (moderate leftist, like a mini-Canada nowadays)
The United States of Montana - (libertarian and progressive, think: Colorado if it migrated northwards)
The Republic of Utah - (libertarian and leftist, not even all that Mormon anymore, Salt Lake City is over 50% agnostic)
The Commonwealth of California - (leftist and elitist, what did you expect?)
The Republic of Cascadia - (leftist and a bit less elitist)
The Republic of Alaska - (moderately progressive, even more "socialist" than Canada)
Canada's economy eclipses the rump USA's economy but not by much, population is much higher and much more south asian/east asian, and the US has had some reorganization.
The Republican and Democratic parties were shamed out of relevance before disbanding, and what replaced them is the Reform Party (purple) and Conservative Party (orange) this also allowed minor parties to gain ground such as the Green Party (guess what color) and the Texas Republican Party (yellow).
There's also a map highlighting freshwater reservoirs in the Republic of Alaska