What restricted the power of King John and created a limited monarchy?

Monarchs had to have some support in order to stay in power. The people either had to be at worst willing to tolerate the king. It helped if the economy was good and the people had jobs. Most kings eventually found themselves controlled in large part by parliament. Many had a constitution or other law which limited their power. In some countries the priests or other officers of the dominant religion have a lot of power over the monarch.