The Europeans suffered the most deadly disease in history when the Bubonic Plague killed most of the Population in Europe.
The Bubonic Plague started in 1347-1351 and returned every decade and stopped returning at about the fifteenth century.
The Bubonic Plague started in Central Asia because people had horrible hygienes and what I mean by that is that they never took showers they probably took showers every few months. They could also get the plague from fleas.
The Plague affected all people, it didn't matter what social class you were in, it still affected you.
The plague affected peasants a lot because of the shortage of workers, they were able to demand a pay raise because people are afraid to work out on the fields.
The peasants obtained power because since people were dying, they would be able to use that as an excuse to demand more. They were able to maintain their power by demanding more money and more rights.