When and how did the peasants of Europe lose their freedom and land?

In the Middle Ages, barbarian kingdoms began to emerge and a feudal-serf system appeared. Then a class of peasants appeared. It was very easy to lose freedom and land in those years. There were three types of peasants: independent (had both freedom and land), tenants (rented land, but were free) and serfs (had nothing). It was easy to turn from an independent peasant into a serf. High taxes and unexpected droughts forced peasants to sell their land in order to survive. They began to rent it for part of the harvest, but for the same reasons they might not have enough funds and they became the serf of the landlord.