We have to remember that spreading "the word" by the sword was not at all unusual back then-- it was the norm in pretty much every major religion. And because it typically involved war, and because the attitude was typically "to the victors belong the spoils", the Crusades were just one manifestation of this.
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I find Christianity was never a major religion, but Christendom was. (remember Constantine) .
Jesus even foretold that MANY would come 'in his name' but prove false at Matthew 7:21-23.
After the death of the apostles genuine Christianity became apostate as per Acts of the Apostles 20:29-30.
False clergy would be fleecing the flock of God for their own interests.
They are in the marriage bed with the political according to Revelation 17:1-2,15.
So, the teachings of 1st-century Christianity became tainted with non-biblical teachings taught as being Scripture.
None of which makes the teachings of Jesus as wrong but makes such wrong teachings as wrong.
We are at the time of Daniel 12:4; Daniel 12:9 when such wrongs are now being exposed.