Before the real plague (bubonic) the land owners would require an animal to be given to them if a male worker died, to compensate them for the lost productivity of the family working the land. During the plague, landowners had such large quantities of animals from this death tax that the remaining workers were able to relocate to places that could pay them well and a middle class was created. Also, the death tax ended. The plague was one of the most potent forces of income equality the world had seen to that point in history.