The Southlands are a crazy-quilt patchwork of nations that really have nothing to do with each other. The most 'cordial' relationship exists between Colorado and the city states of Baja, but the recent conquest of Cabo San Lucas by the Koos has upset the careful balance in the West.
The Legion and Aztland are less nations and more Cults of Personality centered around violence, conquest, rape and madness. Safford is an island of stability in the middle of the Sonora, zombies and all, whereas The Dread Valley is either an oasis of stability or Hell on Earth, depending on your perspective.
How the nations of the Southlands will sort themselves is anyone's guess.