Plot twist: Northern Europe happily kept doing several of its pre-Christian activities. Christianity was superficially conformed to, to avoid repression, but it didn't really supersede as much as add to and slightly change things. For example, while you don't see people actually worshiping the old gods[1], the local version of Easter is filled with the old symbols of fertility, witches, and evil spirits.
[1]: If they ever were ever really "worshiped" in the modern sense, in an animistic belief system.
