What role did the crusades play in the Catholic Church?

Answer 1

They were very important. When Constantinople was being attacked by the Muslims the Pope called a holy war to get the city back to the Christians. Then, the church decided to take back the holy land for Christianity, which failed 7 or 8 times (depending on whether or not you count the children's crusade which mighthave been a myth).

Answer 2

Roman Catholic AnswerFirst a little background, taken from Seven Lies About Catholic History by Diane Moczar:

Unprovoked Muslim aggression in the seventh century brought large parts of the southern Byzantine Empire, including Syria, the Holy Land, and Egypt under Arab rule. Christians who survived the conquests found themselves subject to a special poll tax and discriminated against as an inferior class known as the dhimmi. Often their churches were destroyed and other harsh conditions imposed. For centuries their complaints had been reaching Rome, but Europe was having its own Dark Age of massive invasion, and nothing could be done to relieve the plight of the eastern Christians."

The Crusades were a series of military expeditions over several centuries organized by the peoples of Western Christendom for the recovery of the Holy Places from the Muslims. They were NOT colonialist or commercial ventures, they were not projects of individual war lords, and they were not intended to force Christianity on Jews and Muslims.