On 27 July 1214 the forces of the French king Philip II crushed an army composed of Imperial, English, and Flemish soldiers under the leadership of Otto IV of Germany, ending the 12-year Angevin-Flanders War and destroying England’s Angevin empire.
Back in 1212, Ferdinand, the Infante of Portugal, lost the cities of Aire-su-la-Lys and Saint-Omer under the terms of the Treaty of Pont-a-Vendin. Predictably, he decided he wanted those cities back and created a coalition that included Otto IV, King John I of England, the Duke of Brabant, Count William I of Holland, Duke Theobald of Lorraine, and Duke Henry III of Limburg. Apparently John was in charge of the campaign plan, which focused on drawing Philip south and keep him busy while Otto took the main force and attacked Paris. Unfortunately, John suddenly retreated to his lands in Aquitaine, possibly during one of his fits of depression, leaving the coalition without a clear leader. That wrench in the plan was just enough to give Philip time to amass an enormous army and wheel northward, surprising Otto, who nonetheless decided to fight rather than fall back.
The two forces faced each other east of Bouvines, and after a long day of fighting Otto and his men were forced to withdraw. Hundreds of noblemen and knights were taken prisoner, and thousands of men were killed on both sides. The coalition lost several leaders to either death or capture.
Philip returned to Paris in triumph, while Otto retreated to Harzburg and was soon overthrown as Holy Roman Emperor. John managed to obtain a five-year truce, but his power was so weakened his barons were able to force him to sign the Magna Carta, which limited the crown’s power. Philip went on to conquer most of John’s empire in France, including Anjoy, Brittany, Maine, Normandy, and the Touraine. John was in no position to fight back, and the Angevin Empire was finished.