When England invited a French prince to invade and rule the entire kingdom
In 1216, rebellious English barons, fed up with King John’s refusal to honor Magna Carta, invited Prince Louis of France to take the throne. Louis arrived, captured half the country, and was proclaimed king in London. It was a desperate gamble that nearly ended the English monarchy as it existed.
The First Barons' War (1215–1217) began as a domestic revolt against King John’s despotic rule. After John sealed Magna Carta on 15 June 1215, he quickly reneged on its promises, including Clause 61, which allowed barons to use force against him. Open conflict erupted, and the rebels, seeking a legitimate alternative, turned to Louis, the son of King Philip II of France. Despite opposition from the Pope and his own father, Louis invaded in May 1216, landing in Kent and marching on London, where he was accepted as king by the rebels and citizens alike.
The tide turned with the death of King John in October 1216. His nine-year-old son, Henry III, was quickly crowned, and the royalist regent William Marshal began a campaign to win back the barons. Marshal’s strategy was to offer a moderate path, promising to rule by the principles of Magna Carta while distancing the young king from his father’s failures. As the royalist cause gained momentum, Louis faced military setbacks, most notably at the Battle of Lincoln on 20 May 1217, and the destruction of his reinforcement fleet in the Battle of Sandwich.
By September 1217, the war concluded with the Treaty of Lambeth. Louis agreed he had never been the legitimate king, surrendered his remaining strongholds, and departed England. The conflict was a pivotal moment in medieval history, shifting from a struggle over the king's authority to a dynastic war for the throne. It solidified the role of Magna Carta as a foundational document, as the regents for Henry III reissued it to secure the loyalty of the nobility and restore order to a fractured realm.
Source: First Barons' War
