What helped to instigate the start of the crusades (as well as all the other crusades) and could you possibly recommend some scholarly articles, books and essays on the topic?
Thank you, Classic Apricot
There were many reasons for the Catholic church to launch such an unprecedented experiment. If we take the most primary source we have on the subject, which would be the the speech of the Pope Urban II, it would clearly state that a Crusade would serve as: 1. Pilgrimage for all the faithful to the Holy Land; 2. The only way to offer military help to the Eastern Roman Empire.
We can take the first statement at face value because we know (from the history of the crusades themselves), that the knights and the lay people participating in the Crusade have shown a great deal of religious fanaticism. In the context of well-known medieval religiosity, an offer from the Pope to forgive all your sins if you travel to Jerusalem (and plunder the richest empires of Europe on your way there) couldn't be easily turned down.
I personally do not believe that the Pope would benevolently provide help to the Byzantines, especially after a very rough break-up in 1054. If there is any evidence that it was the case, I am not aware of it.
When it comes to the "untold" reasons for the Crusades, mainstream medieval history has a consensus that they were undertaken as a continuation of "Peace of God" policies and as a manifestation of the Gregorian reforms. First, "peace of god" didn't achieve much when it was instituted a century earlier. Constant warring between fractured principalities in France and Germany, between secular and ecclesial feudal lords continued even after the "Dictatus Papae", that has been conceived especially to end the conflict of inheritance surrounding possessions of the Church. Therefore, the only way for the feudal Europe to win time for consecutive consolidation of ecclesial and secular power was to channel "the feudal violence" into Anatolia and Palestine. Later we can see the involvement of the Italian city-states as a proof for the existence of underlying economic interests, but there are now studies that I am aware of that explain the economic side of the Crusade phenomenon.
here is my list of books on the subject:
Andrew Jotischky, Crusading and the Crusader States, New York: Routledge, 2013 (Recovering the Past).
Paul E. Chevedden, "Pope urban II and the ideology of the crusades", in The Crusader World, ed. Adrian J. Boas, New York: Routledge, 2016.
Joshua Prawer, The Latin Kingdom of Jerusalem... (I only have a french version, sry)
Sorry for such a short list. It's just that I mostly read articles and I mostly read them in french and russian. Tell me what languages you can read and maybe I'll give you some of them
u/ElDidall has got you on the right track already, but there are a couple of older answers that might help as well:
See those for some more sources!