Easy, it all comes down to money, so the banking clan was naturally involved as it served their purposes of subjugating people into weaklings, combined with jewy long term infiltration tactics.
It was basically a combination of killing the hard opposition through crusades and general pagan executions, yes the crusades happened outside sandnigger lands too, for example Finland was crusaded multiple times, and then playing the long game of converting people.
Church modified their holy celebrations to match pagan holidays and slowly took over.
Eventually the systems reached a critical mass and ran under it's own weight. People became their own jailors and took virtue in being a weakling.
Thankfully the slave religion is fucking off, as younger generations don't really give a shit about it and now church has to result to propping up their numbers with niggers.