In summer 1195, a marriage between Louis and Eleanor of Brittany niece of Richard I of England was suggested for an alliance between Philip II and Richard, but it failed. It is said that the Emperor Henry VI opposed the marriage; and the failure was also a sign that Richard would replace Arthur, younger brother of Eleanor, as heir to England with his only living brother, John. This soon led to a sudden deterioration in relations between Richard and Philip.  On 23 May 1200, at the age of 12, Louis was married to Blanche of Castile, following prolonged negotiations between Philip Augustus and Blanche’s uncle John of England (as represented in William Shakespeare’s historical play King John).  In 1214 King John of England began his final campaign to reclaim Normandy from Philip II Augustus. John was optimistic, as he had successfully built up alliances with the Emperor Otto IV, Count Renaud of Boulogne and Count Ferdinand of Flanders. John’s plan was to split Philip’s forces by pushing north-east from Poitou towards Paris, whilst Otto, Renaud and Ferdinand, supported by William Longespée, marched south-west from Flanders. Whereas Philip II Augustus took personal command of the northern front against the emperor and his allies, he gave his son Louis the command of the front against the Plantagenet possessions in middle France. The first part of the campaign went well for the English, with John outmanoeuvring the forces under the command of Prince Louis and retaking the county of Anjou by the end of June. John besieged the castle of Roche-au-Moine, a key stronghold, forcing Louis to give battle against John’s larger army. The local Angevin nobles refused to advance with the king; left at something of a disadvantage, John retreated back to La Rochelle. Shortly afterwards, Philip II Augustus won the hard-fought battle of Bouvines in the north against Otto and John’s other allies, bringing an end to John’s hopes of retaking Normandy.

In 1215, the English barons rebelled in the First Barons’ War against the unpopular King John of England (1199–1216). The barons offered the throne to Prince Louis, who landed unopposed on the Isle of Thanet in eastern Kent, England at the head of an army on 21 May 1216. There was little resistance when the prince entered London and Louis was proclaimed King at St Paul’s Cathedral with great pomp and celebration in the presence of all of London. Even though he was not crowned, many nobles, as well as King Alexander II of Scotland (1214–49) for his English possessions, gathered to give homage.  On 14 June 1216, Louis captured Winchester and soon controlled over half of the English kingdom.[9] But just when it seemed that England was his, King John’s death in October 1216 caused many of the rebellious barons to desert Louis in favour of John’s nine-year-old son, Henry III.  With William Marshal acting as regent, a call for the English “to defend our land” against the French led to a reversal of fortunes on the battlefield. After his army was beaten at Lincoln on 20 May 1217, and his naval forces (led by Eustace the Monk) were defeated off the coast of Sandwich on 24 August 1217, he was forced to make peace on English terms. In 1216 and 1217 Prince Louis also tried to conquer Dover Castle but without success.  The principal provisions of the Treaty of Lambeth were an amnesty for English rebels, Louis to undertake not to attack England again, and 10,000 marks to be given to Louis. The effect of the treaty was that Louis agreed he had never been the legitimate King of England.

On 1 November 1223, he issued an ordinance that prohibited his officials from recording debts owed to Jews, thus reversing the policies set by his father Philip II Augustus. Usury (lending money with interest) was illegal for Christians to practice; according to Church law it was seen as a vice in which people profited from others’ misfortune (like gambling) and was punishable by excommunication, a severe punishment. Since Jews were not Christian, they could not be excommunicated and thus fell into a legal grey area that secular rulers would sometimes exploit by allowing (or requesting) Jews to provide usury services, often for personal gain to the secular ruler and to the discontent of the Church. Louis VIII’s prohibition was one attempt at resolving this legal problem, which was a constant source of friction in Church and State courts.  Twenty-six barons accepted, but Theobald IV (1201–53), the powerful Count of Champagne, did not, since he had an agreement with the Jews that guaranteed him extra income through taxation. Theobald IV would become a major opposition force to Capetian dominance, and his hostility was manifest during the reign of Louis VIII. For example, during the siege of Avignon, he performed only the minimum service of 40 days and left for home amid charges of treachery.

The Albigensian Crusade had begun in 1209, ostensibly against the Cathar heretics of southern France and Languedoc in particular, though it soon became a contest between lords of northern France and those of Occitania in the south. The first phase from 1209 to 1215 was quite successful for the northern forces, but this was followed by a series of local rebellions from 1215 to 1225 that undid many of these earlier gains. There followed the seizure of Avignon and Languedoc.  In 1225, the council of Bourges excommunicated the Count of Toulouse, Raymond VII, and declared a renewed crusade against the southern barons. Louis happily renewed the conflict in order to enforce his royal rights. Roger Bernard the Great, Count of Foix, tried to keep the peace, but the king rejected his embassy and the counts of Foix and Toulouse took up arms against him. The king was largely successful, taking Avignon after a three-month siege, but he did not complete the conquest before his death.  While returning to Paris, King Louis VIII became ill with dysentery, his doctors introduced a virgin in his bed, thinking that sexual stimulation would cure him. The king gently dismissed the girl, saying that he had never seen such a pretty healer but that he preferred to die than to commit a mortal sin. He died on 8 November 1226 in the Château de Montpensier, Auvergne.  The Saint Denis Basilica houses the tomb of Louis VIII. His son, Louis IX (1226–70), succeeded him on the throne. Louis IX concluded the crusade in the south in 1229.