Louis VIII gained military experience while still heir to the French throne. In 1214 he confronted King John of England at La Roche-aux-Moines, helping defeat the invasion of his father Philip II's territories. English barons rebelling against John invited Louis to claim their crown. He landed in England in 1216, entered London and received the allegiance of many opponents of the king. He was proclaimed king but never crowned, and his claim faced papal opposition.

John's death in October changed the struggle: his young son Henry III offered the barons an alternative to a French ruler. Louis continued the campaign, but his supporters lost at Lincoln in May 1217. A naval defeat off Sandwich that August cut off reinforcements. Under the resulting peace settlement Louis abandoned his English claim and withdrew. He later campaigned in the Albigensian Crusade, connecting Capetian expansion with the war against heresy in southern France.

Succeeding Philip in 1223, Louis renewed pressure on the English possessions in France. In 1224 he gained Poitou and La Rochelle, reducing the territory held for Henry III. He launched another southern crusade in 1226, securing Avignon after a prolonged siege and extending royal administration through newly established officials. Many southern towns submitted as his army advanced. On the return journey he fell ill and died at Montpensier in November 1226. Blanche of Castile became regent for their son Louis IX.