The Hundred Years' War
2.2 Context: Dukes of Burgundy
Philip the Bold did not just become a prince. In 1363 he received from his father, King John II (John the Good), the Duchy of Burgundy as an apanage (a duchy for a younger son of the king). In 1369 he married Margaret of Male, the heiress of the Count of Flanders. This gave him enormous wealth and power (Flanders, Artois, Franche-Comté, etc.). He was a younger brother of the future King Charles V, who died early.
This made him the founder of the Burgundian branch of the House of Valois, which grew into a major European power.