What was a military effect of the fall of the Western Roman Empire?

The Huns united to take the city of Rome.
The Eastern Roman Empire became unstable and fell, too.
The people reestablished the military and fought back.
The empire could not defend its borders against more invasions.

Which course of action did president carter propose in order to solve this problem for the next generation? a. contract with foreign nations to build wind turbines b. reduce federal spending on solar cell energy research c. drill fewer offshore wells to conserve marine life d. develop alternative energy sources