Second Barons' War

The Second Barons' War (1264–1267) was a civil war in England between the forces of a number of barons led by Simon de Montfort, against the Royalist forces led by Prince Edward (later Edward I of England), in the name of Henry III.

Causes
The reign of Henry III is most remembered for the constitutional crisis in this period of civil strife, which was provoked ostensibly by Henry III's demands for extra finances, but which marked a more general dissatisfaction with Henry's methods of government on the part of the English barons, discontent which was exacerbated at a more popular level by widespread famine.

French-born Simon de Montfort had originally been one of the foreign upstarts so loathed by many lords as Henry's foreign councillors, but having inherited through his mother the English title Earl of Leicester, he married Henry’s sister Eleanor with Henry's permission, but without the agreement of the English Barons, since it was a matter of the state: a feud developed between the two. Their relationship reached a crisis in the 1250s, when de Montfort was put on trial for actions he took as lieutenant of Gascony, the last remaining Plantagenet lands across the English Channel.

Henry also became embroiled in funding a war against the Hohenstaufen in Sicily on behalf of Pope Innocent IV in return for the Hohenstaufen title King of Sicily for his second son Edmund. This made many barons fearful that Henry was following in the footsteps of his father King John and, like him, needed to be kept in check. When Henry's treasury ran dry, Innocent withdrew the title, and in regranting it to Charles of Anjou in effect negated the sale.

Simon, earl of Leicester, became leader of those who wanted to reassert the Magna Carta and force the king to surrender more power to the baronial council. In 1258, initiating the move toward reform, seven leading barons forced Henry to agree to the Provisions of Oxford, which effectively abolished the absolutist Anglo-Norman monarchy, giving power to a council of twenty-four barons to deal with the business of government and providing for a great council in the form of a parliament every three years, to monitor their performance.

Henry was forced to take part in the swearing of a collective oath to uphold the Provisions of Oxford. In the following years, those supporting de Montfort, including his circle of Franciscan advisors centered on Adam Marsh, and those loyal to the king grew more and more polarised; Henry obtained a papal bull in 1261 exempting him from his oath, and both sides began to raise armies, the Royalists under Edward Longshanks, Henry's eldest son. A civil war followed.

Course of the war
The charismatic de Montfort and his forces had captured most of southeastern England by 1263 and at the Battle of Lewes in 1264, Henry was defeated and taken prisoner by de Montfort's army. While Henry was reduced to a figurehead king, de Montfort broadened parliamentary representation to include groups beyond the nobility, members from each county of England and many important towns. Henry and Edward continued under house arrest. The short period which followed was the closest England was to come to complete abolition of the monarchy until the Commonwealth period of 1649–1660, and many of the barons who had initially supported de Montfort began to suspect that he had gone too far with his reforming zeal.

Only fifteen months later de Montfort's gains were reversed when Edward Longshanks escaped captivity to lead the royalists into battle again, defeating and killing de Montfort at the Battle of Evesham in 1265. His son, Simon, attempted a negotiated surrender but it was rejected by de Montfort loyalists. The impasse culminated in the six-month Siege of Kenilworth at which the King prevailed. De Montfort's forces were permitted to leave the castle with their weapons and horses.

Following this victory, savage retribution was exacted on the rebels and authority was restored to King Henry. The casualties of the war are estimated at 15,000.

Timeline

 * 1261 – King Henry III of England obtains a papal bull releasing him from the Provisions of Oxford
 * 1264 – Before May – The war officially begins.
 * 1264 – 14 May – The Battle of Lewes is fought between Simon de Montfort, 6th Earl of Leicester, and King Henry III of England in Sussex. By the end of the battle, de Montfort's forces capture both King Henry and his son, future King Edward I, making de Montfort the "uncrowned king of England".
 * 1265 – 20 January – In Westminster, the first English parliament conducts its first meeting in the Palace of Westminster, now also known as the Houses of Parliament.
 * 1265 – 28 May – Future King Edward I of England escapes captivity at the hands of Simon de Montfort, 6th Earl of Leicester.
 * 1265 – 4 August – The Battle of Evesham is fought in Worcestershire, with the army of Edward defeating the forces of rebellious barons led by Simon de Montfort and killing de Montfort and many of his allies.
 * 1266 - Unknown date - The Battle of Chesterfield is fought in Cheshire, with the  royal army defeating the forces of the Earl of Derby.
 * 1266 – October – The war winds down as supporters of the slain Simon de Montfort make an offer of peace to the king in the Dictum of Kenilworth.
 * 1267 – The war ends, as the rebels and King Henry III of England agree to peace terms as laid out in the Dictum of Kenilworth.