Ummm - not to get people riled, however, I will point to the situation in the late 11th Century when the First Crusade was initiated and launched.
The fledgling states in Europe were in a state of internal political turmoil, but were beginning to sort themselves out a bit. Constantinople was beginning to bend under fairly steady expansion of Islamic forces (military as well as cultural and religous) into Byzantium - having already engulfed Palestine, and with it, Jerusalem. Like it or not, there were actions taken by Muslims against Christian residents and pilgrims because they were Christians. Given the choice to convert or be enslaved, or executed if they were soldiers or other men with military training, some chose to convert (sowing the seeds for current problems in the Balkans) others refused.
Pope Urban saw this as an opportunity to do a several things at once. First, this was a chance to get some of the younger sons of the nobility who had no future, a chance to make a name for themselves without making war in Europe. Second, it was an opportunity to aid Constantinople, who actually called for assistance from the Western Church, as fellow Christians in spite of the schism between them. Finally, and most importantly (to Urban) from waht I have read, this was an opportunity to open Jerusalem to Christian pilgrims, allowing them to travel relatively safely.
People now talk about excesses that resulted in that time. By current standards, they certainly were excessive. By contemporary standards, they were only excessive as far as the side that lost were concerned. It is important to note that while the First Crusade was a military success (the captured Jerusalem and established a Christian kingdom), this was the result of Christian residents of, and pilgrims to Jerusalem, being treated with excessive harshness, by THEIR standards (although the Muslims did not see things quite that way).
Now then, the later Crusades were hardly that inspired or successful. When Jerusalem was retaken by the Seljuk Turks, the Second Crusade was launched, and failed miserably. The Third Crusade featured Richard III, King of England, travelling to Palestine, losing the military campaign, but winning a stunning victory at Jaffa, and negotiating a treaty to allow pilgrims to travel freely. The Fourth and Fifth Crusades did absolutely no one any good - with the Fifth Crusade weakening Constantinople, setting it up to eventually fall in battle in the late 15th Century (or was it early 16th, memory is unclear).
The Crusades were a response to the early struggle to expand the faith is Islam. They briefly checked it in the East. Charles "Martel" stopped it cold in Spain.
Oh, the word struggle translates litterally as "jihad".
As far as President Bush using the word "crusade", I think his handlers should limit the stuff he ad-libs on.
Now, back to work -
Regards - Pete