Which event marked the beginning of the Hundred Years' War?

The beginning of the Hundred Years' War is marked by the death of a French king, Charles IV, in 1328. His death led to a succession crisis because he left no male heir, which created a dispute over the French throne. The conflict centered around Edward III of England, who claimed the throne due to his maternal lineage, and the royal family of France, which opposed this claim. This dispute triggered the series of conflicts known as the Hundred Years' War, which lasted from 1337 to 1453 and involved several key battles and shifting allegiances between the two nations.

In contrast, the Battle of Hastings occurred in 1066, marking a pivotal moment in English history but well before the Hundred Years' War. The signing of the Magna Carta in 1215 established certain legal principles in England but did not directly relate to the war. The outbreak of the Black Death in the mid-14th century also falls outside the timeline of the war's beginning, although it impacted the later war dynamics and society in general. Thus, the death of Charles IV serves as the crucial catalyst for the onset of hostilities between England and France, making it the correct answer.