Rome faced constant attack after the pax romana because its army

A. was becoming less loyal to the emperor.

Explanation:

This is the main reason why Rome faced constant attack after the Pax Romana. One of the most important qualities of the Roman Empire was its large, well-organized army. This allowed Rome to become extremely powerful and to conquer a very large territory. However, such strength can only exist as long as the army is disciplined and dedicated. If the army does not trust the emperor, then it is likely that their performance will be worse and that the empire will become easier to attack.

to extend a country’s power and influence

the answer i chose to believe is 'harmony'