Europe changed in so many ways after the Crusades occured. First, intellectual development. It changed in its ways of doing things, new ideas came up to them, clothes, etc. after seeing and passing among all those unfamiliar people. It resulted in the great period of the Renaissance in the end. It also changed in commerce, they started building shops and brought back lots of goods from the middle east like perfumes, spices, pearls, etc. and started trading with other countries. Last but not least, Feudalism. The king's power increased, it became absolute power and the feudal power decreased.
Other changes were in the Catholic Church, like the tithe. 1/10 of your money goes to the church. Another thing that caused alot of changes in Europe was the Voyages of Discovery, the people became inspired to go out and travel to see the world.
I think the most important change was the commerce.
