What caused the collapse of the Roman Empire?

Invasions by Barbarian tribes. The most straightforward theory for Western Rome's collapse pins the fall on a string of military losses sustained against outside forces. Rome had tangled with Germanic tribes for centuries, but by the 300's “barbarian” groups like the Goths had encroached beyond the Empire's borders. These are the causes and effects of the falling of the Roman Empire: External military threats were a major cause of Rome's fall, and its effects spread across the empire. ... After Rome was divided, a powerful group known as the Huns began moving west, their numbers growing with captured prisoners and new allies. People from all walks of life were eager to reap the rewards of war.

Explanation: I hope this helped.

it further strained relations between the north and the south and convinced

b, the anti immigrant fervor