The Barons of England were angry with the King and eventually rebelled against him because he over-taxed them for his unproductive wars in French territory and forced him to sign the Magna Carta which limited his power as King.
They eventually gained leverage because the English monarchy needed money to pay ransom for John's brother who was abducted and made prisoner by Emperor Henry VI and to fund the Crusades.
I would try inequalities in the tax structure. The rich were paying less but getting more out the system. Poor could not even buy food. (Let them eat cake.)
