Final answer:
The French government's substantial financial aid to the American colonists during their fight for independence significantly contributed to France's large debt under Louis XVI, which was a factor leading up to the French Revolution.
Step-by-step explanation:
One reason that France's debt under Louis XVI was so large is D. The French government had helped fund the American Revolution. Financial strains, including those from the costs incurred from the Seven Years War, were exacerbated by substantial contributions to support American colonists in their struggle for independence. These expenditures put additional pressure on France's already strained finances.
In an attempt to resolve this economic crisis, King Louis XVI called the Estates-General in 1789, with the intent of implementing tax reforms to manage the soaring national debt. However, financial mismanagement and opposition to raising taxes by the privileged Estates compounded the problems, culminating in the outbreak of the French Revolution. The revolution brought more financial challenges, with demands for social welfare, and attempts by the monarchy to quell the unrest further draining the royal treasury.