Final answer:
The Gupta Empire faced difficulties with incompetent emperors, tax collection, and repelling the Huna tribe.
Step-by-step explanation:
The empire that had a series of incompetent emperors who struggled to collect taxes and fight off the invading Huna tribe was the Gupta Empire. The Gupta Empire, which ruled over northern India from the fourth to the seventh centuries CE, faced significant challenges, especially during its decline. The Hephthalites, also known as the White Huns, were notably responsible for the downfall of the remnants of the neighboring Kushan Empire in the fifth century and posed a threat to the stability of the region.