I'm curious to as how much of a role did the early catholic church have in spreading christianity throughout europe. Was it mostly done voluntarily, were there forced conversions and conquest? Islam is stereotypical claimed to have spread through "conquest by the sword", would this be an accurate characterization of how christianity spread throughout Europe?
Hey! There's a lot more that can be written, but since you've asked about the role of the early Church in the dissemination of Christianity throughout Europe, an older post of might be of interest. I don't touch on Charlemagne or the Crusades unfortunately, but it still might be of some help :)
Could you narrow the scope at all? The process of Christianizing Europe lasted over a millennia and in a wide variety of cultural contexts. While there are some broad trends that can be talked about, do you have a specific time or place in mind?
Oh, I found one more, and I think it's well worth reading: "Why was Christianity able to convert the whole of Europe? What about it made it so successful compared to older, native, religions?" by /u/talondearg .
More can be written, but you might like some previous discussions on the early spread in FAQ section "The Rise of Christianity" by /u/talondearg and the participants in "AMA - History of Western Christianity".
This is not to discourage discussion. More questions, data, and debate are welcome.