Why did King John lose Normandy to France?

King John lost Normandy to France primarily due to a combination of political missteps, military failures, and the superior resources of the French crown.

The conflict was ignited in 1200 when John married Isabella of Angoulême, who had been betrothed to Hugh IX de Lusignan, a powerful vassal in Poitou. This action provoked a rebellion among the Lusignan family, who appealed to Philip II, John’s feudal overlord for his French territories. When John refused to appear before Philip’s court to answer for his actions, his French lands were declared forfeit, leading to war.12

While John achieved a temporary victory at Mirebeau in 1202, his position was undermined by the suspicious death of his nephew and rival claimant, Arthur of Brittany, and the eventual fall of the strategic fortress Château Gaillard in 1204. Ultimately, the loss was driven by the superior resources of the French monarchy and the increasing strain on the military and financial capabilities of England and Normandy. By 1204, Normandy had collapsed, and by 1206, John had lost Anjou, Maine, and parts of Poitou.12