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Campaigns in Brittany, Toulouse and the Vexin

Henry had a difficult relationship with Louis VII of France throughout the 1150s. The two men had already clashed over Henry's succession to Normandy and the remarriage of Eleanor, and the relationship was not repaired. Louis invariably attempted to take the moral high ground in respect to Henry, capitalising on his own reputation as a crusader and circulating malicious rumours about his rival's ungovernable temper. Henry had greater resources than Louis, particularly after taking England, and Louis was far less dynamic in resisting Angevin power than he had been earlier in his reign. The disputes between the two drew in other powers across the region, including Thierry, Count of Flanders, who signed a military alliance with Henry, albeit with a clause that prevented the count from being forced to fight against Louis, his feudal lord. Further south, Theobald V, Count of Blois, an enemy of Louis, became another early ally of Henry. The resulting military tensions and the frequent face-to-face meetings to attempt to resolve them have led the historian Jean Dunbabin to liken the situation to the 20th-century Cold War in Europe.

On his return to the Continent from England in the 1150s, Henry sought to secure his French lands and quash any potential rebellion. To this end, in 1154 Henry and Louis agreed to a peace treaty, under which Henry bought back Vernon and Neuf-Marché from Louis. The treaty appeared shaky, and tensions remained — in particular, Henry had not given homage to Louis for his French possessions. They met at Paris and Mont-Saint-Michel in 1158, agreeing to betroth Henry's eldest living son, the Young Henry, to Louis's daughter Margaret. The marriage deal would have involved Louis granting the disputed territory of the Vexin to Margaret on her marriage to the Young Henry: while this would ultimately give Henry the lands that he claimed, it also implied that the Vexin was Louis's to give away in the first place, in itself a political concession. For a short while, a permanent peace between Henry and Louis looked plausible.

Meanwhile, Henry turned his attention to the Duchy of Brittany, which neighboured his lands and retained strong traditions of independence. The Breton dukes held little power across most of the duchy, which was mostly controlled by local lords. In 1148, Duke Conan III died and civil war broke out. Henry claimed to be the overlord of Brittany, on the basis that the duchy had owed loyalty to Henry I, and saw controlling the duchy both as a way of securing his other French territories and as a potential inheritance for one of his sons. Initially Henry's strategy was to rule indirectly through proxies, and accordingly, Henry supported Conan IV 's claims over most of the duchy, partly because Conan had strong English ties and could be easily influenced. Conan's uncle, Hoël, continued to control the county of Nantes in the east until he was deposed in 1156 by Henry's brother, Geoffrey, possibly with Henry's support. When Geoffrey died in 1158, Conan attempted to reclaim Nantes but was opposed by Henry who annexed it for himself. Louis took no action to intervene as Henry steadily increased his power in Brittany.

Henry hoped to take a similar approach to regaining control of Toulouse in southern France. Toulouse, while traditionally tied to the Duchy of Aquitaine, had become increasingly independent and was now ruled by Count Raymond V. The rulers of Aquitaine had made tenuous claims on the county by hereditary right; Henry now hoped to claim it on Eleanor's behalf, and encouraged by her, Henry first allied himself with Raymond's enemy Raymond Berenguer of Barcelona and then in 1159 threatened to invade himself to depose the Count of Toulouse. Louis married his sister Constance to the Count in an attempt to secure his southern frontiers; nonetheless, when Henry and Louis discussed the matter of Toulouse, Henry left believing that he had the French king's support for military intervention. Henry invaded Toulouse, only to find Louis visiting Raymond in the city. Henry was not prepared to directly attack Louis, who was still his feudal lord, and withdrew, contenting himself with ravaging the surrounding county, seizing castles and taking the province of Quercy. The episode proved to be a long-running point of dispute between the two kings and the chronicler William of Newburgh called the ensuing conflict with Toulouse a "forty years' war".

In the aftermath of the Toulouse episode, Louis made an attempt to repair relations with Henry through an 1160 peace treaty. This promised Henry the lands and the rights of his grandfather Henry I; it reaffirmed the betrothal of Young Henry and Margaret and the Vexin deal; and it involved Young Henry giving homage to Louis, a way of reinforcing the young boy's position as heir and Louis's position as king. Almost immediately after the peace conference, Louis shifted his position considerably. His wife Constance died and he married Adèle, the sister of the Counts of Blois and Champagne. Louis also betrothed daughters by Eleanor to Adèle's brothers Theobald V, Count of Blois, and Henry I, Count of Champagne. This represented an aggressive containment strategy towards Henry rather than the agreed rapprochement and caused Theobald to abandon his alliance with Henry. Henry, who had custody of both Young Henry and Margaret, reacted angrily, and in November he bullied several papal legates into marrying them—despite the children being only five and three years old respectively—and promptly seized the Vexin. Now it was Louis's turn to be furious, as the move clearly broke the spirit of the 1160 treaty.

Military tensions between the two leaders immediately increased. Theobald mobilised his forces along the border with Touraine. Henry responded by attacking Chaumont in Blois in a surprise attack and took Theobald's castle in a siege. At the start of 1161 war seemed likely to spread across the region until a fresh peace was negotiated at Fréteval that autumn, followed by a second peace treaty in 1162, overseen by Pope Alexander III. Despite this temporary halt in hostilities, Henry's seizure of the Vexin started a second long-running dispute between him and the kings of France.