In eastern Europe, where lords had colonized vast areas of Steppe in the High Middle Ages, peasants were essentially free from feudal levies prior to the Black Death. Landowners were only able to persuade peasants to live on their estates by offering them extremely favorable terms.
I find this dynamic interesting. Serfs are "free" in the sense that they can travel to different parcels of land and offer themselves for work. Once on that land, they are expected to make food for the owner of that land. The food would then be consumed by the owner and any surplus (not eaten by the owner and the serfs themselves [their allotted amount]) would go to market and be sold for profit. This system kept vassals accountable - they had to protect and treat the serfs "well-enough" so that they would be abe to make a profit off their hioldings.
