Final answer:
The Hundred Years' War was a series of conflicts between England and France from 1337 to 1453, with both nations being the main combatants.
Step-by-step explanation:
The key participants in the Hundred Years' War were England and France. This prolonged series of conflicts took place from 1337 to 1453, as both nations struggled over territorial claims and the right to the French throne. During this time, both England and France were shaping up as nation-states and frequently found themselves at odds with each other. The Hundred Years' War had a significant impact on the development of both countries and influenced their future, including their delayed participation in New World exploration, as they dealt with their own domestic issues and political dynamics, including the Protestant Reformation.