European society was extremely hierarchal during the middle ages and in some ways the Plague removed some of these societal boundaries. Before the plague nobles held land (therfore power), they were often times clergy or at least closesly associated with the clergy. They would collect taxes from the peasants and power would always stay within families because of constructs like paterfamilias.
Life was extremely difficult for peasants during the middle ages. They had no access to education and were limited to mostly farm/merchant work. They were oftentimes exploited and oppressed by the nobles through taxes. Peasants were also under extreme rule by the church. They had no say in the laws governing them.
It is well known that the plague killed a third, if not half of the European population. As the plague swept through Europe. Nobles ran away to their manors while the peasants were left to die in their small villages. The lack of hygeine let the plague run rampant through villages killing entire families. Some nobles managed to escape the plague by running to their remote houses but this did not always work. This did not always work however and some of the most powerful people perished. An example of this is the death of British princess Joan (see Articles and Explanation) page.
Overall anarchy consumed Europe. Bodies had to be taken away by carriages, and entire cities were consumed by the plauge and its after effects.