On May 12, 1039, this proclamation by King Henry I became the trigger for the war.

For William, the title of Duke of Normandy and the territory of the Duchy can never be lost, it is not only a property and rights, but also a kind of sustenance for William's hometown and father Robert, and if he loses Normandy, William will become a rootless duckweed, so this declaration of King Henry I William is absolutely unacceptable.

Despite this, William did not give up his efforts, and sent an envoy of the nobles to Paris to meet Henry I, asking him not to ally with the Count of Erbourg and not to invade Normandy.

But regrettably, Henry I refused, without any hesitation, and said: "Go back to Normandy quickly, go and tell William, and get ready for battle!" ”

The matter was irreparable, and William officially issued a war mobilization order, ordering the assembled troops in each territory to go to the front, and at the same time mobilizing the serfs of the various estates as conscripts, so that they could transport food and baggage for William's army.

William divided his army into three fronts, with the front facing the Count of Castle on the east side led by the Count of Richard, and Baron Andrew as his lieutenant to guard the eastern Normandy line.

William did not ask the Eastern Front to achieve anything, after all, this army was only a knightly order formed by the knights of Rouen, Evre, and Urburg, not a professional army.

At the same time, they had to face an army of the king's vassals led by Gautier, Count of Amiens-Wissan and his brother Raoult, including the Count of Amiens-Wiisan, the Count of Vimanduc, the Archbishop of Reims, the Count of Sens, the Count of Berry, and many other nobles, totaling more than 18,000 people, including 3,300 French knights and heavy cavalry, and more than 5,600 heavy infantry, which was a very large army.

Their goal was to support the Count of Urburg's rebellion, leading him to attack Rouen, the heart of Normandy, with the minimum goal of attracting William's attention and building fighters for the King's army in the center.

In order to increase his chances of victory, William immediately contacted his ally the Duchy of Flanders and asked Duke Baldwin V to immediately send troops to support us.

However, according to the reply received by William, Duke Baldwin V was obviously selfish, and he led an army of 15,000 men to garrison the capital Bruges, and had no intention of marching at all.

Obviously, Duke Baldwin V wanted to watch the fire from the other side, and watch King William and Henry I fight against each other, so as to reap the benefits of the fisherman.

The reason why Baldwin V did this was also very clear to William, in the final analysis, it was because William and Normandy expanded so rapidly that it aroused the jealousy of Duke Baldwin.

The Duchy of Normandy now possessed a vast area of northwestern France, a prosperous economy, and William had at his disposal an army of the most warlike Normans, a powerful military combined with a large territory and great wealth, and it was not only Henry I who felt threatened by Normandy, but also Baldwin V.

As for King Henry I, who was also a threat to the Duchy of Flanders, Baldwin V was not too worried, they Low Dutch had lived in this land for hundreds of years, and what Duke of Flanders had not fought against his king? On another occasion when the Duchy of Flanders suffered a defeat? In the end, Flanders was not unharmed.

On the western road of Normandy, Count Rodrigo had returned to Fort Affranche, in the Countdom of Morten, with his Second Legion and the Knights of Morten, where he would face an army of 15,000 men of the Duchy of Anjou, led by Joufroois, Duke of Anjou.

The army of the Duchy of Anjou had lost nearly 1,000 knights in the war two years earlier, and although they had recovered well in the past two years, the number of knights had not recovered the most sonic morale of the year, of which 1,300 were knights at most, 3,800 heavy infantry, and the rest were mostly conscripted infantry with weak combat effectiveness.

On the battlefield of the Duchy of Brittany, the Knights of Enman were left by Rodrigo to consolidate the occupied counties of Domonia and Broleck, and to clean up the sporadic rebellions of the Duchy of Brittany, while the remaining two sides, the Count of Leon and the Count of Koneff, could only retreat to their respective castles after their main forces were annihilated, and they would not have survived until now if it were not for the time-consuming capture of the castle and the current emergency.

William was not at all worried about the eastern battlefield controlled by Count Rodrigo, but the Duchy of Anjou could not defeat Count Rodrigo, who was good at war.

However, if the alliance of nobles of the Duchy of Poitu sent by the Duke of Aquitaine joined the eastern battlefield, a difficult battle would be inevitable.

William was most worried about the elite royal army led by Henry I of the Kingdom of France and his allied army of vassals, as well as the army of the Dukes of Champagne led by Thibault, Duke of Champagne.

This army was huge, and the most effective of them was the elite king's army, which consisted of local knights in Paris and Orleans, mercenary knights and mercenaries, squire knights and descendants of knights, and knights from all over France who volunteered to join the French king's command, each of whom had strong personal combat power, and was good at horse and foot combat, and it was arguably the most powerful army outside of William's Praetorian Guard.

This elite royal army of 15,000 men was led by General Dugan, a close general of Henry I, and had more than 5,000 knights and heavy cavalry, 5,000 heavy infantry, 2,000 light infantry, and 3,000 Genoese crossbowmen.

In particular, the 3,000 Genoese crossbowmen were specially prepared by Henry I to deal with William's Norman longbowmen, and in the Battle of Donvron, two years ago, the longbowmen's performance was experienced, and the knights and heavy infantry who died under the longbowmen were countless, so Henry I was very afraid of the Normandy longbowmen.

In addition to the elite royal army, the Duchy of Champagne led by the Duke of Champagne was also not to be underestimated, although he only took out a mere 12,000 men to participate in the battle, but the 1,800 knights included were still quite threatening.

As for the last 10,000 or so recruited from the noble vassals of Henry I and the vassals of the city, they were the least combat-ready of the allied army, without any knights and heavy cavalry, and the only three hundred cavalry were also the caravan escort riders of the merchants.

This levy was led by the mayor of Paris, and they would play the role of baggage soldiers and cannon fodder, all the dirty work was theirs, and in the end they had to accept the death, but they did not dare to resist in front of Henry and his army, as if they had accepted their fate.

The war began, and King Henry I, as the leader of the coalition, led a coalition of 37,000 men along the west bank of the Seine to the county of Evreux, the hinterland of Normandy.

Henry I had long coveted the richest county in the Duchy of Normandy, so the first target he chose was Evre.