Given a disfluent sentence, modify the sentence to it to its equivalent fluent form, preserving the meaning of the sentence.

When was the Ming dynasty in power no change this to when did the Yuan people suffer a series of natural disasters?

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
user
When did the Yuan people suffer a series of natural disasters?