How did the plague weaken the system of feudalism in europe?

The system of feudalism needed a lot of workers, who were tied to the land, and had to deliver a part of their harvest to their lords. The farmers generally had a poor life and struggled to make enough both for themselves and for the lords, but the lords benefited from this, as they had many farmers paying them a part of their harvest

Before the plague, the land was scarce, but people plenty, which meant that the farmers could not set conditions on their work. After the plague the number of farmers decreased, and there was a lot of work needed, so the farmers could search for a different place to work, if the feudal lords were demanding too much,.