Answer:
After the invasions from Germanic tribes who were fleeing from the Mongols, Europeans sought protection as their homes were destroyed. They allied themselves with people who had large amounts of land, who were kings. These kings passed their lands to lords, who in return managed a territory and were loyal. These lords would then give land to knights, who in return provided protection for everyone. Peasants were given land to work on. This exchange of land, or fiefs, for services is the underlying basis of the feudal system in Europe. Basically the need of protection lead to the development of feudalism.