On 21 May 1420, Henry V of England and Charles VI of France agreed on the Treaty of Troyes.

The treaty made Henry regent of France and heir to the French throne. He was also to marry Charles’s daughter, Catherine of Valois. On paper, it was an extraordinary settlement. Henry had turned military success into a claim of lawful succession.

That was the point of the treaty. English power in France was no longer presented only as conquest. It was presented as an inheritance, a marriage and a royal agreement.

The settlement was weaker than it looked. Charles VI’s illness had damaged the French kingship, and France was divided by civil conflict. Henry’s success depended on those divisions as well as English arms. The Burgundian faction accepted him, but the Dauphin Charles, the French king’s son, was excluded from the succession.

That exclusion was the treaty’s central weakness. The Dauphin did not disappear because a document had pushed him aside. He still had supporters, and many in France had no reason to accept an English king as their future ruler.

The arrangement also depended heavily on Henry himself. In August 1422, he died before Charles VI. When Charles died soon afterwards, the claim passed to Henry VI, who was still a baby.

Troyes marked the high point of Henry V’s ambition in France. It promised a double monarchy, with England and France held by one king. It also showed how unstable that settlement was. The treaty created a legal claim, but it did not create a settled rule.