According to this Bill Warner, PhD video, the Crusades were a response to Jihadist expansion. This other, unnecessarily snarky guy has a critique of the modern pop-culture understanding as espoused by Crash Course.
What's the historian consensus on this topic? Is there one?
From FAQ: https://www.reddit.com/r/AskHistorians/wiki/middleages#wiki_motivations_for_the_crusades
Just to point one thing out, a cursory search suggests that Bill Warner's Ph.D. is in Physics and not, in fact, history, which makes me pretty wary of him. This is not to say that people with Ph.D.s outside of history can't be reliable sources (this subreddit has quite a few!) its just that most of them would not (I expect) bring up their unrelated Ph.D. in discussions of history. It suggests a fallacious appeal to authority.
Someone asked a similar question earlier today and the response they got was a nice summary of the reasons for the start of the First Crusade If you have further questions you can ask me, or the individual who answered that previous post, and I'm sure we'd be happy to try and provide some more answers.
I'm not particularly inclined to watch either video, I'm a little busy so I don't have time honestly, but if you have any specific points in them that you would like addressing I'd be happy to have a go at them if you tell me what they are.
hi.. just ran into your post. This video generated a few questions several months ago; check out this one:
and you may be interested in a few more related posts on similar claims
I saw this article about the Crusades posted on Facebook. How accurate are the bullet points?
Was Jihad, in the modern sense of the word, a reaction to the cristhian crusades?
As for that FAQ section, /u/ambarenya's response is generally regarded as a high quality answer.