The Hundred Years War was an armed conflict between the kingdoms of France and England, which lasted 116 years (May 24, 1337 -19 October 1453) of feudal origin, since its purpose was to resolve who would control the enormous possessions accumulated by English monarchs since 1154 in French territories, due to the accession to the English throne of Henry II Plantagenet, Count of Anjou. It ended with the English withdrawal of French lands.
To narrow down the research context, you could ask:
What European powers will fight in this war?
What were the factors that led these powers to war?
Why the war lasted a long period in time?
Who were the outstanding characters of this contest?
What consequences did this war bring for the powers and for all of Europe?