DBWI: Religously homogenous Europe

Europe is one of the world's most religiously diverse regions, with Asatrú, Romuva, Rodism, Hellenism, Druidism, Mithraism and Sol Invictus only being a handful of it's religions with followers in the millions, of course there are also a lot of minor religious groups, notably the Judeo-Christians that can be found spread out all over the continent, but that are the majority in very few places.

What would it take for Europe to be religious homogenous? Variations within the religion can still be a thing, but it should still be identifiable as the same core religion. My best shot is a roman empire that survives atleast into the 5th century and manages to enforce some kind of state religion, but that may be unlikely since they were such a tolerant bunch.
 
Maybe if the Roman Empire hadn't collapsed in the 3rd century? It may have allowed one of these religions - let's say Manichaenism (because Manichaenism is cool! And it doesn't get enough attention) - gets a later Emperor's ear abd he enforced it as a new state religion.

Extra points if this Emperor is able to save Romania from a nasty period of decline and use the new faith to knit the empire togrther

Not sure how likely this is though, since Roman was in petty bad shape in the 3rd century snd I'm not sure there was any saving it by that point.
 
Very difficult. Most of the religions in Europe were only codified in the last 200 years when nation-states emerged.

Theoretically, the Romans had spread their pantheonic religion to all corners of the continent only for mystery cults and local derivations to return as they always had. The same with the Goths, Vikings, Slavs and Khazars and for that matter Hispanius Karoly's army. Almost every conquest failed to enforce its religion with few exceptions.
 
Top