Hi, three weeks late, but I just ran into this post while hunting down something, so thought I'd throw you a link:

A great place to start is the FAQ section The Crusades | Cause and Motivation, particularly the first post, Who started the Crusades? (Each one) by /u/Ambarenya

The posts in there have all been long archived, so if you have follow-up questions for any of the users, just ask here and tag their username to notify them.