Which reason for the fall of Rome do you believe is the most significant in the collapse of the empire, why

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 300s “barbarian” groups like the Goths had encroached beyond the Empire's borders.

the indians crossed artificial boundaries, setting the stage for conflict