One of the factors that led to the fall of Rome was

invasion.

Explanation:

1.. 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 border

Invasions by Barbarian tribes

Explanation:

answer; i believe the correct answer is (the willamete valley);