It created the atmosphere for the eventual end of Feudalism. The massive amount of killing turned the peasants and serfs from a widely available resource into a much more coveted workforce. It gave the peasants the economic power to leave and go to a different Lord who would offer better rates/land/payment. While serfs were still forced to stay in their holding, they had more power, as they were less easily replaced. This would eventually contribute to the collapse of the feudal system, as strip farming (splitting a field into small strips of land each owned by a different family) gave way to whole field farming, due to the deaths of the owners of many strips. These larger farms allowed families to make more money from their land, both allowing for capitalist styles of money-making from farming, and increasing crop yields. This led to an increase in people heading towards towns and cities, as they could get more readily available food sources from the new larger farms. I have condensed a couple of centuries into one paragraph here, these changes were not overnight and did not happen at the same time.