For almost two years, William and his Normans did not use force to expand abroad, because he knew very well that unless a miraculous opportunity arose, the expansion of force had reached its limit, and if it was used by force, it would not be strange to be besieged by the whole European country.

Force was only one of the means of asserting the king's power, and the Norman jurisprudence that developed under William's auspices could also serve his expansion and centralized rule.

William, who is well versed in history, knows very well that if he encounters an incompetent or mediocre king, then the royal family's territory may be taken away by foreign monarchs or domestic vassals, wealth may also be wasted by extravagant monarchs, and in a powerful government, it may also be eaten up by internal enemies, and only by leaving a law sufficient to protect the interests and rule of the Normandy family can the Normandy royal family continue.

By 1055, the legal system of the Norman kingdom had been initially perfected, including civil law, criminal law, tax law, military law, aristocratic law, and so on.

But this was still not enough, and William had discovered from some recent events that the Norman kingdom needed a law that regulated the relationship between the powers and duties of noble vassals and monarchs, that is, feudal law.

William was surrounded by dozens of legal experts who worked for him and had been assisting him in codifying and strengthening a legal empire that even the largest princely realms in the Norman kingdom could not leave without this network.

When compiling the feudal law, the basic law of the kingdom, William proposed a basic principle: the king should owe allegiance to anyone.

For example, if a city belongs to the local bishop, and William takes over the city, he does not need to owe allegiance to the bishop.

When jurists describe the principalities and princely states of the Norman kingdom, the princely states they refer to as subordinate possessions, which require the grant of the king.

In order to strengthen the royal power, the jurists suggested that at the conferral ceremony, the vassals should swear allegiance to William, and clearly state the obligations they need to bear, and if the vassals neglect or fail to fulfill their obligations as a vassal, William, as the king, can ask the vassals to compensate him, and even take back all the territories of the vassals on this ground.

In 1200, Lucion of the Kingdom of France and Hugo IX, Count of La Marche (in the same family as Lucioni of the Heavenly Dynasty), wanted to find a marriage for his son Hugo X, and he fell in love with Isabella, the only daughter of the nearby Count of Angoulême, and his heir.

If his son Hugo X had been able to marry Isabella, his family would have been able to form a sizable vassal state in western France.

At that time, the southwestern territories of Farah, including Poitou, Aquitaine, and Gascony, as well as the rich Anjou and Normandy, were the family fiefdoms of the Plantagenet dynasty.

At that time, England was ruled by John, the younger brother of Richard the Lionheart, who was incompetent but cruel, and saw that his vassal Lucion and Hugo IX, Count of La Marsh, wanted to become bigger, which was a threat to John, so he took the lead and married Isabella in August 1200, although the latter was already engaged to the Lusignan family.

Although Lucioni's Hugo IX swore allegiance to the "landless king" John, who was his feudal lord, King John's brutal behavior of robbing his relatives was regarded by Count Hugo as a betrayal of him by the feudal king.

So Hugo IX sent a letter to the then King of France, Philip. Augustus II asked for help.

Philip II saw an opportunity to dismember the Plantagenet dynasty and immediately agreed to Hugo IX's request to convene a court in Paris to ask King John to appear before him.

At that time, although King John was the king of England, he occupied a large number of territories in Normandy, Anjou, Poitou, Aquitaine and Gascony, accounting for almost the size of the Kingdom of France, and Philip II's royal territory was not as large as that of King John.

These territories of King John in France were granted by the King of France, and were therefore subject to vassalal obligations.

At that time, several monarchs of the Plantagenet dynasty, whether it was its founding monarch, Henry II of Plantagenet, or later Richard the Lionheart, claimed king of England in the north and the king of France on the other, as did King John.

Philip II demanded that King John fulfill his obligations as a vassal and go to Paris to stand trial, but King John refused to appear on the grounds that he had imposed vassalage obligations on Philip only because of Normandy.

Eventually, under the auspices of Philip II, the court in Paris finally handed down a verdict in the absence of King John, and for refusing to fulfill his obligation to seal the city, he was sentenced to "confiscate all the fiefs that he had received from the king", a term that came to be called commise.

King John, of course, did not obey the verdict, so the war began, and the incompetent, mediocre and brutal King John was naturally not the opponent of King Philip II of France, who was respected as "Augustus", and after several battles, the English army was defeated, and a large area of Normandy, Anjou, and Poitou were taken away by Philip II, and finally the Plantagenet Dynasty's territory in the Kingdom of France was left with only part of Aquitaine and the territory of the Duchy of Gascony.

At the time, such a decision to repossess all the domains for non-compliance by a vassal was rare, and it was unprecedented, but it was not unfounded, and Philip II followed the aristocratic custom of dealing with vassals' betrayals: when a vassal betrayed, the vassal could take possession of his land and castle.

Philip II regarded King John's failure to fulfill his vassal obligations as a betrayal and confiscated all his possessions, which was far-fetched but reasonable.

William also made this point: when a feudal city refused to fulfill its feudal obligations, it could be regarded as a betrayal, and the king, as a sovereign, had the right to take back all the domains of the vassal.

In the new Feudal Law of the Norman Kingdom, the jurists not only greatly increased the power of the king according to William's wishes.

The first of these is the power to confiscate the territory of vassals who refuse to fulfill their obligations and rebellious vassals.

Correspondingly, the feudal law stipulates the service obligations that should be fulfilled by each closed city.

For William, who had a strong standing army, service was already secondary, but he still made strict rules.

William not only ordered the court officials to compile a list of knights in charge of the defense of a certain castle, which detailed the list of nobles to be served in each place, who were required to serve in the army at their own expense, according to the size of their fiefdoms, and served in the army for forty days, or could also pay the military tax corresponding to their fiefdoms, known as the "shield tax".

The strict feudal obligations of vassals enumerated in feudal law made it impossible for vassals to evade the fulfillment of their obligations.

Of course, William was more interested in the economic and political benefits obtained through feudal law, as well as the influence and control of his vassals.