Following its defeat in the First Civil war, the United States of America gradually weakened, unable to adapt to having a second major power sharing the continent with it. Miraculously, the nation survived into the 20th century, finally falling apart in 1931 AD. The effect was so massive, it also brought about the collapse of the Confederacy and nearly that of Canada. By the end of the 20th century, the scene was set for the Dominion war.
Note: This is a sort of alternative history of the Many Nations of North America, with a few changes such as instead of fighting themselves, the former United States nations must fight the ultra-religious dictatorship of the Dominion of Canada.