Why did the death of John the Fearless help Henry V gain a Burgundian alliance?

The death of John the Fearless on September 10, 1419, was a pivotal moment that solidified the alliance between Henry V and the Burgundian faction.

John the Fearless had been engaged in a bitter civil war against the Armagnac faction, which supported the dauphin (the future Charles VII). Although John had previously explored negotiations with Henry V, he had also attempted to reach a peace settlement with the dauphin to unite against the English. During a meeting on the bridge of Montereau intended for such a reconciliation, John was assassinated by the dauphin’s followers.123

Following this murder, John’s son and successor, Philip the Good, sought to avenge his father. Driven by this desire for retribution against the dauphin, Philip formally allied himself with Henry V in December 1419. This alliance paved the way for the Treaty of Troyes in 1420, which disinherited the dauphin and recognized Henry V as the heir to the French throne.31