The First Barons' War (1215–1217) was a civil war in the Kingdom of England in which a group of rebellious major landowners (commonly referred to as barons) led by Robert Fitzwalter waged war against King John of England. The conflict resulted from King John's disastrous wars against King Philip II of France, which led to the collapse of the Angevin Empire, and John's subsequent refusal to accept and abide by the Magna Carta, which John had sealed on 15 June 1215.
The rebellious barons, faced with an uncompromising king, turned to King Philip's son, Louis, who, in 1216, then sailed to England with an army despite his father's disapproval, as well as the pope's, who subsequently excommunicated him. Louis captured Winchester and soon controlled over half of the English kingdom. He was proclaimed "King of England" in London by the barons, although never actually crowned.
Louis's ambitions of ruling England faced a major setback in October 1216, when John's death led to the rebellious barons deserting him in favour of John's nine-year-old son, Henry III, and the war dragged on. Louis's army was finally beaten at the Battle of Lincoln on 20 May 1217. Also, after a fleet assembled by his wife, Blanche of Castile, attempted to bring him French reinforcements but was defeated off the coast of Sandwich on 24 August 1217, he was forced to make peace on English terms. He signed the Treaty of Lambeth and surrendered the few remaining castles that he held. The treaty had the effect of Louis agreeing he had never been the legitimate king of England. That formalised the end of the civil war and the departure of the French from England.
Background
King John in June 1215 was forced to put his seal to "The Articles of the Barons" by a group of powerful barons who could no longer stand John's failed leadership and despotic rule. The king's Great Seal was attached to it on 15 June 1215. In return, the barons renewed their oaths of fealty to King John on 19 July 1215. A formal document to record the agreement was created by the royal chancery on 15 July: this was the original Magna Carta. "The law of the land" is one of the great watchwords of Magna Carta by standing in opposition to the king's mere will.
The Magna Carta of 1215 contained clauses that theoretically noticeably reduced the power of the king, such as Clause 61, the "security clause", which allowed a group of 25 barons to override the king at any time by way of force, a medieval legal process called distraint that was normal in feudal relationships but had never been applied to a king. After a few months of half-hearted attempts to negotiate in the summer of 1215, open warfare broke out between the rebel barons and the king and his supporters.
Course of events
French intervention
The war began over Magna Carta but quickly turned into a dynastic war for the throne of England. The rebel barons, faced with a powerful king, turned to Louis, the son and heir apparent of King Philip II of France and the grandson-in-law of King Henry II of England. The Norman invasion had occurred only 149 years before, and the relationship between England and France was not as simply adversarial as it later became. The contemporary document, the Annals of Waverley saw no contradiction in stating that Louis was invited to invade to "prevent the realm being pillaged by aliens."
At first, in November 1215, Louis simply sent the barons a contingent of knights to protect London. However, even at that stage he also agreed to an open invasion, despite the discouragement from his father and from Pope Innocent III. That came in May 1216, when watchmen on the coast of Thanet detected sails on the horizon, and on the next day, the King of England and his armies saw Louis's troops disembark on the coast of Kent.
John decided to escape to the Saxon capital of Winchester, and so Louis had little resistance on his march to London. He entered London, also with little resistance, and was openly received by the rebel barons and citizens of London and proclaimed (though not crowned) king at St Paul's Cathedral. Many nobles gathered to give homage to him, including Alexander II of Scotland, who held fiefs in England.
Many of John's supporters, sensing a tide of change, moved to support the barons. Gerald of Wales remarked: "The madness of slavery is over, the time of liberty has been granted, English necks are free from the yoke."