The most accurate response regarding the development of France as a nation-state is:
"France developed into a nation-state after the Hundred Years’ War ended with the French under a single kingdom through conquest."
This period, particularly the conclusion of the Hundred Years’ War in the 15th century, marked significant centralization of authority under the French crown, contributing to the emergence of a unified French identity. The war strengthened national consciousness and laid the groundwork for future political and social cohesion that would define France as a modern nation-state.