In 1420, the Treaty of Troyes was signed. It named Henry V, the King of England, as heir to the French throne. He also married Catherine, the French King's daughter, that same year. In 1421, he returned to France for a second campaign, dying suddenly in 1422, as a result of dysentery contracted during the Siege of Meaux.
What if Henry V had lived? He was only thirty-five at the time of his death, and he died two months before Charles VI. Would Henry have managed to keep France and England united until he passed the titles onto his successor? How long would they have remained united?