In 1215 CE King John signed The Magna Carta. This document said that the king could still rule but had to consult the barons and the church when changing the tax laws. King John also agreed that nobody take a persons rights!
The Bubonic plague was a very deadly disease and killed many people! which means a lot of workers died. Resulting in a higher demand of pay from workers.
The Bubonic Plague was being carried by rats from the trade ships, because they were traveling to china and bringing back disease.
The Hundred Years War helped to shift the power from feudal lords to monarchs and to common people.
Resulting in less need for the Nobles to supply the Kings with Knights.