The best explanation of the role external forces played in the Ming Dynasty’s fall is:
The expense of fighting external forces weakened the empire as new groups, such as the Jurchen (later known as the Manchus), gained control.
This response captures the idea that the Ming Dynasty's military engagements and the resources devoted to defending against external threats, like invasions and piracy, strained the empire's economy and contributed to its vulnerability, ultimately facilitating the rise of the Manchus and the fall of the Ming.