1204 – Philippe Auguste takes the fortress of Château-Gaillard after a 6-month siege, this victory opens the door to Normandy. The capture of Château-Gaillard had an important impact, Jean Sans Terre had left for England without having made any serious attempt to defend this highly strategic fortress and left the Normans defeated. Philip Augustus then embarked on a campaign to subjugate the entire province. Rouen, its capital, is a centerpiece which, for three centuries, the kings of France have often come up against.  For his part, his Breton ally, Guy de Thouars, acting as Duke of Brittany, attacked Normandy from the west. He conquered Mont Saint Michel, the traditional border between Brittany and Normandy, and set it on fire, a dramatic destruction at the time but which would later allow the reconstruction of the masterpiece of Gothic art: "The Wonder".
April 25 –  Birth of Louis of France, 4th son of Louis VIII and Blanche of Castile, Count of Artois.
On 2 May, the beginning of the final phase of the conquest, Philippe Auguste cut Rouen off from his rear by taking, in a few days, several localities: Pont-de-l'Arche, La Roche-Orival, Neubourg,  Moulineaux and Montfort-sur-Risle. The Flemish Roger de Gouy surrendered Argentan on 7 May, then Falaise fell on the 14th, after a 7-day siege, Caen, which sheltered the Seneschal of Normandy, was taken practically without a fight on the 21st. Philip Augustus pursued him to Rouen, where he had taken refuge, and began the siege towards the end of May. Rouen,  commanded by Pierre de Préaux, assisted by the elite of the barons of the neighborhood, was ready to sustain a long siege, and yet.......
On 1 June,  the city signed an agreement stipulating surrender in the event of failure or lack of relief within the next thirty days. Arques and Verneuil-sur-Avre joined this agreement, thus linking their fate to that of Rouen.
On 24 June, Rouen surrendered without a fight, fearing that in the event of too long a resistance, it would lose the commercial advantages it enjoyed for the besieged. Philip Augustus razed the old ducal castle and the walls to the ground and undertook the construction of a new fortress, the new royal officers showed arrogance towards the population. Mainland Normandy now belongs to the crown of France. Lacking the fleet he needed, Philip Augustus forgot the Channel Islands, which remained under the control of the Kingdom of England.  
1206 – John Lackland, known as John Landless, King of England, has not given up resuming, through diplomacy by asserting feudal customs by virtue of which "a land confiscated by an overlord from his vassal can be restored to him if the latter repents", or by arms, his confiscated continental lands, which Philip Augustus does not envisage.
1213 – On 8 April, Philip Augustus convenes an assembly in Soissons, where Ferrand of Portugal demands, once again, the restitution of two towns  Saint Omer and Aire-sur-la-Lys that had been appropriated by Prince Louis, Count of Artois. Faced with the refusal, he left with a bang and turned to John the Landless and the Emperor Otto of Brunswick, whose vassal he was by virtue of his title of Count of Hainaut.
In the conflict between Pope Innocent III and Emperor Otto of Brunswick and John the Landless, both of whom were excommunicated, Philip Augustus appeared as the pope's natural ally.
On 15 May, the alliance was reversed, and John the Landless was reconciled with the pope. Philip Augustus then had to face a vast coalition, including in addition to John the Landless, Emperor Otto IV of Brunswick, Renaud of Dammartin, Ferrand of Flanders, Thiébaud I of Lorraine, Henry I of Brabant, William I of Holland and Philip II of Courtenay-Namur.
On 30 May, hostilities began, Philip Augustus' fleet concentrated at Damme (before the port of Bruges) was largely destroyed, thus jeopardizing a possible invasion of England.
1214 – The emperor invades the kingdom of France from the north, John Landless goes up from Aquitaine to the Loire, Philip Augustus must divide his forces.
On 2 July, Crown Prince Louis' army put to flight that of Jean Sans Terre at La-Roche-aux-Moines (near Angers).
On 27 July,  Philip Augustus, at the head of the royal army, of which the Normans represented only about 5% of the troops, met the coalition at Bouvines (near Lille), the emperor was put to flight, the imperial eagle captured, Ferrand of Portugal and Renaud de Dammartin taken prisoner, Jean Sans Terre was not present. The questioning of the conquest of Normandy in 1204 was now very difficult.
In September,  when a five-year truce was signed at Chinon, Philip Augustus realized that he could only defeat John by invading England.

1215 – John Landless is in the grip of a revolt of the barons, as a result of his defeats on the continent, he has to concede to them "the Magna Carta".
1216 – In May, Crown Prince Louis arrives in England to seize the crown of England offered by the English barons in revolt against John the Landless.
On 19 October, John the Landless died, Henry III, aged 9, succeeded him and the English gathered around him, Louis renounced the crown of England.
1217 – On May 20, Louis' army is routed at Lincoln, England.
On 24 August, the fleet carrying new troops was destroyed between Calais and Sandwich.
On 11 September, under the hospice of the papal legate, a truce was concluded at Chinon (Indre et Loire).
1220 – Philip Augustus obtains the renewal of this truce for another five years.
1223 – On July 14, Philip Augustus dies in Mantes without having carried out his plan to invade England, the Norman aristocrats will not recover their property there.
August 6 -  His son Louis succeeds him at the age of 36 and becomes Louis VIII the Lion. Defeated in England, Louis is said to have promised to return the continental possessions of John Landless to the 16-year-old Henry III, who did not give up any of his claims.
1224 – The resumption of war is inevitable.
1226 – On November 8, Louis VIII the Lion dies in Montpensier (Puy de Dôme). The minority of his successor Louis IX (the future Saint Louis) led to a resurgence of the conflict that did not spare Normandy.

The consequences of the annexation of Normandy
Philip Augustus, who had conquered Normandy on the basis of feudal law, was determined to keep it in the royal domain. To do this, it must secure the loyalty of the ruling class, which owns property on both sides of the Channel.

Nobility
In 1204, the Norman nobility consisted of about two thousand knights, including about sixty barons, about ten of whom had the title of "count". Norman feudalism was not very hierarchical, few of the duke's vassals had vassals themselves, the duke dominated feudalism directly. The attachment of Normandy to the kingdom of France essentially solicits the high baronage, the upper echelon of the aristocracy. He had to choose between two vassal commitments: the one due to the Duke of Normandy, King of England or the one due to the duke's overlord, the King of France.Philip Augustus invited him to choose between him and the King of England, those who wanted to keep their Norman lands had to renounce their island possessions and pay him homage by renouncing any feudal ties with John Landless,  within a maximum period of one year expiring in April 1205, a period extended until Christmas 1205. Among the few exemptions were, among others, William the Marshal, Earl of Pembroke, Robert de Fontenay, Eleanor de Vitré and Alix, Countess of Eu. John Landless, for his part, demanded the presence of his vassals at his side on pain of confiscation of their property. The choice of fief for the Anglo-Norman lords was dictated solely by its importance outside of any connection with either party. The majority of the great barons preferred England, as did 5 to 10% of the rest of the nobility. Philip Augustus then issued a new rule confiscating Norman lands on the death of a lord if his nearest heir resided in England. This rule, applied until the reign of Saint Louis, creates inextricable legal situations in the event of a disputed inheritance. The lands of the Normans who chose England were attached to the crown's estates.

The Administration

The Duchy of Normandy continues to exist in texts and facts, the king continues to refer to it, but never bears the title of Duke of Normandy . There was no longer an enthronement ceremony specific to Normandy, when he was consecrated, he became de facto Duke of Normandy. In addition, the office of Seneschal of Normandy, governor of the country during the duke's presence abroad, was abolished. Philip Augustus maintained the "Norman custom", in particular, because it was more advantageous for the sovereign, in feudal and criminal matters, than that of France. He modified a few points to make the Normans equal to the French, particularly in the matter of duelling, by removing the privileged position of the appellant.
On the judicial level, the Sovereign Court of the Exchequer was maintained, symbolising the independence of Normandy, while undergoing major overhauls. It is now presided over by royal commissioners. These councillors, who came from Paris, were unfamiliar with the Norman custom, and they systematically referred it to the king as soon as a complicated case arose. Bailiffs, high officials appointed, paid by the king and foreign to the duchy represented him in the areas of administration, justice and the summoning of the army. They were the superiors of the other royal agents in Normandy, the viscounts, provosts and sergeants, most of whom were Normans.