During the decline, the Roman army had been severely weakened to the
point where invaders that could have previously been defeated by the
Empire were eventually able to destroy it. Ultimately, the Roman Empire
collapsed because of "the general failure of its armies to perform the
tasks that were required of them." One reason for the breakdown of the
army was that the Roman legions would fight in civil wars over their
choices for Emperor because they were unhappy with the weaker Emperors
that were frequent in the later Roman Empire. "These struggles served as
an irresistible invitation to German and other enemies to break into
the distracted provinces." Although the civil wars served as a
distraction to the Roman army, the wars also had a detrimental effect on
the army because they damaged its manpower, both in quality and
numbers.
The Roman army during this time was divided into the high
quality soldiers, called the field force, and the lower quality
soldiers, referred to as the frontier force, who did not fight as much
as the field force. The frontier force was mainly deployed to local
garrisons that were not as volatile as the places where the field forces
fought. Because of the civil wars between the legions and the battles
against outside invaders and enemies of the Western Roman Empire, the
field force was considerably weakened and greatly reduced in number.
The field force had to take second-rate soldiers from the frontier
force, thus lowering the quality of the army. The waning quality of the
Roman army was not its only concern; there were also not a sufficient
number of new soldiers being drafted. all the info is in there thank litpick.com i didnt write this
