King John had been forced to sign the Magna Carta, but his son, Henry III, pretended it didn't exist. Simon De Montfort, the French born Earl of Leicester who was also married to the king's sister, lead a revolt to confirm and expand the rights in the Magna Carta. De Montfort reached out to commoners to help defeat Henry III, while the king bribed barons with confiscated land to switch sides. The revolt ironically became a rising of commoners against all foreign born noblemen. In 1265, Simon De Montfort called the first English Parliament to include commoners. De Montfort was killed in battle later on in 1265. Henry III’s son, Edward I, made it a habit to call commoners to parliament in 1297. Without Simon De Montfort fighting for the Magna Carta, I don't think it would be considered as important a precedent as it is today. Prior to De Montfort's organized resistance to Henry III, the Magna Carta was a dead letter.
Our rights required defenders, and still do. Freedom is not free.
Article on Magna Carta (requires subscription)
http://www.wsj.com/articles/magna-carta-eight-centuries-of-liberty-1432912022#lf_comment=318079386