No offense but I find you using the phrase "Islamic hordes" incrediably narrow minded and offensive and borderline racist.
Why are you focusing solely on Islam? What about Maoism? Buddhism? Shintoism (and even more worse in my opinion) twisted 'christian' cults?
How about loving people first and foremost regardless of what they believe in? You aint going to make many friends let alone lead others to Christ by calling other peoples 'hordes' as if their some kind of savage.
Speaking as a history student - do you know what the early christian church and govt did to convince people to join the crusade? Money and lost christian relics that the muslims were supposedly 'harbouring.' People believed them and hundreds of thousands of innocent women and children and decent men were murdered who could have been quietly converted by normal missionaries who could have tried to adapt Christianity into their culture like with the Celts and Vikings. Preventing the spread of Islam is total bull. During that period in history the entire middle east was a hub of peace compared to the tiny country of Rome on its own. While the East were gaining sophiscated technology and methods of travel and exploring, Europe was learning new ways of killing each other and how to spread the plague.
Not sure what Maoism or Shintoism is, but Buddhism (and I'm guessing the other two) don't seem to expand as quickly as islam. If you look at the rate of expansion, islam was created in 600 or so? And within a few centuries islam and the empires that were formed from it controlled the bottom half of the mediteranean including large parts of Spain, parts of Sicily and large parts of formerly byzantine territory(yeah I knwo thats general... sorry) That's pretty rapid expansion & threat to christian Europe.
The Crusade was a response to a request by the Byzantine empire for the (I think... plz correct me if I'm wrong, it's been a while since I've read this stuff) for help against the turks as they were putting a lot of presure on them. For a visual thing this is the map of the Byzantine empire before the first crusade -
http://en.wikipedia.org/wiki/File:Byzantiumforecrusades.jpg I can't find a pic of after the first crusade but you can imagine the extent of territory they reclaimed considering where the crusader states were formed. - It set islam back a long way, it isn't as well known but there were also crusades into Spain which helped reclaim territory there.
Also... just on this point Kiwi "People believed them and hundreds of thousands of innocent women and children and decent men were murdered who could have been quietly converted by normal missionaries who could have tried to adapt Christianity into their culture like with the Celts and Vikings." I'm pretty sure that under islamic rule at that time you were not allowed to preach christianity & there was harsh punishment for doing so... They tolerated and permitted other religions in the places they conquered but they did not permit them to preach the gospel or try and convert muslims to christianity... Correct me if I'm wrong though i'm not 100% on this.
So were the crusades a response to islamic aggression and expansion? Well... in my opinion yes although there were other political forces involved of course & I've seen it argued that the first crusade was just a papal grab for power. Don't really agree with taht one myself... I think it was motivated by religion.
I will agree with you on the point that there would have been false reasons given to the population to convince them to go and preaching 'salvation for an armed pilgrimage' was definately wrong of the church. Anyway, it's far too late & I'm probably going to wake up in a few hours and think what the heck did I write so I'm going to sleep.
Overall in my opinoin it was motivated my christianity but it wasn't exactly christian in the way in which it was conducted... dunno. Fascinating period of history though.
PS: Also, the plague wasn't until later
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