Why did the Roman Empire decline? Select all correct answers.

Germanic tribes, Parthians, and North Africans pressed attacks against the empire's frontiers from all sides.

A series of brutal and incompetent emperors squandered huge sums and led to public disgust with the imperial government.

Budget deficits caused by low taxes on Roman citizens led to increased public debt and helped topple the central government.

Roman troops returning from the Middle East brought a plague into the capital that killed up to 10 percent of the city's population.