Long story short? After they get defeated in a Holy War in Denmark and have yet another holy site of theirs burned by the Solarians (TTL's stand-in for Christians), a bunch of volva, gothi and other priests all around the lands that still worship the ancient Norse religion band together in Uppsala and reform their religion into an organized religion so they can survive against Solarianism. Something similar later happens with the Baltic people in Prussia, Lithuania and Latvia but like, a couple centuries later /skip






