IIRC, Martin Luther, after he had read the Scriptures (which apparently were chained to the altar in certain Churches - since only the elite Priests could - in some instances - read them, they got to "interpret" them as they saw fit... or to advance their agendas.) he confronted the establishment elite of the Roman Church, and soon found himself under a "Holy Roman Fatwah" being hunted down like an animal.
Had he not been able to hide out in a freind's remote mountain castle, he probably would not have lasted long.
After Luther's open Gospel theory met the Guttenburg press, the Bible became available in the "people's language", so that the priests were no longer able to manipulate the populations and governments with their "creative interpretations" of it.
Sort of like our current "Law", always written in convoluted "Legaleze", and Lawyers/Judges, wouldn't you say?
The political dominance of the RCC went into decline after that, and people began converting to Christianity because they WANTED to, not just to keep themselves and their Families from being tortured and/or killed.
From my admittedly limited reading of History, for a while there around the various Crusades, there seems to have been precious little distinction in terms of how people were treated - especially dissidents from "the Faith" - between Muhummedean and "Christian".
People who wanted to live out their lives to a natural conclusion worshipped whatever or whoever the guy holding the sword over your neck did.