Final answer:
The main accomplishment of Louis IX was that he largely ended the continual feuding and wars among French nobles, contributing to the centralization of power in France. correct option is C.
Step-by-step explanation:
One of the main accomplishments of Louis IX, who reigned as King of France, was his effect on domestic peace and administrative reforms. Specifically, option C is correct: He largely ended the continual feuding and wars among French nobles. This was part of a broader centralization of power in the French monarchy which started under Philip II and was indicative of the growing strength and resource control of the monarchs in the early fourteenth century. Nevertheless, while Louis IX had great influence during his reign, it is worth noting that the accomplishment listed in the question should not be confused with those of Louis XIV, who later reigned from 1643 to 1715 and who had a significant impact in establishing France as an absolute monarchy and in utilizing art and architecture as expressions of monarchical power.