Crusades in the Middle Ages played a very important role in the fate of the Middle Ages. The crusades brought cultural diffusion which introduced new ideas, like technology and intellectual advances, along with desires for luxurious goods. Because of this, the crusades were able to put an end to the Middle Ages.
Feudalism played an important role in the Middle Ages because it helped protect all of Western Europe's people, from peasants to the King. Because of how dangerous the Middle Ages were, the king would offer land to knights, in exchange for their protection. The king also use the manorial system to allow peasants to farm on his land, in exchange for part of the food from their harvests.
Roman Catholic was very important in the Middle Ages. It was the only thing that united Western Europe's people since they didn't have a government. People believe in Medieval Christianity allowed people to stay loyal and obedient to the church, this was very important because this too helped keep people united and helped things remain peaceful for the time being.