Complex sentence: When Charles IV died without male heir, the senior lineage of the House of Capet ended; he was succeeded by his cousin Philip of Valois, but the contested legitimacy was one factor of the Hundred Years' War.
Split into simpler sentences: When Charles IV died without male heir, the senior lineage of the House of Capet ended. He was succeeded by his cousin Philip of Valois, but the contested legitimacy was one factor of the Hundred Years' War.