From the steam workshop page

After the End is a total conversion mod and successor to the popular CK II mod, bringing Crusader Kings III to the post-post apocalyptic Americas. Covering all of the Americas, After the End takes place long after a great cataclysm, the Event, wiped out of modern society. Centuries later new neo-medieval societies have risen from the ashes.

The year is 2666 and new empires, faiths and cultures have filled the void left over. The Empire of Brazil is the largest in the world, though it still struggles to control the Amazon basin. Further north, Alineados and Cristeros struggle over control of the Mexican Empire. The Emperor of the Holy Columbian Commonwealth claims descent from old America - though the Americanists believe only their religious leaders can truly claim that. Out west, the Eternal Living Guru of California has secured his position at the head of numerous faiths, though many fiercely resist his rule. Play as any of these great powers and reshape the Americas in your image, or one of the numerous smaller dynasties that have arisen across the Americas.