The two armies that met in the battle were led by King Henry III of England and a rebel leader, Simon de Montfort, 6th Earl of Leicester. Henry III's son, Prince Edward, fought on his side. The battle came about because many of the leading noblemen of England were unhappy with the way King Henry was ruling the country. They wanted more involvement in the government. The Barons voted to hold a Parliament regularly so that they could discuss subjects such as taxation. King Henry would not agree to this, and so both sides started to raise armies. When the two sides met at Lewes two days before, Simon de Montfort tried to arrange a truce with the king. King Henry refused and so both sides got ready to fight a battle. 