The Magna Carta was a charter signed by King John of England in 1215 that limited the power of the monarchy and established basic legal rights. It forced the king to respect the rights of nobles and commoners by preventing him from raising taxes or disrupting the church without permission. The Magna Carta came about due to King John's unpopularity from military defeats and imposition of new taxes, which angered the nobles. They forced him to sign the Magna Carta establishing constitutional principles that still influence legal systems today.