Overstretching led to a reliance on foreign troops
From the late second century onwards Rome’s politics were burdened by the need to maintain an enormous military to protect its borders. The military became an enormous tax burden many emperors struggled to pay for, due in part to Rome’s worsening economic problems.  The overexpansion of the Roman military led to the incorporation of barbarian peoples into the army. Increasingly foreign foederati were used to supplement the legions. These Germanic recruits were an undisciplined shadow of the old Roman legion. The Romans even tried to solve the problems of a mass invasion by adopting the Goths into their army. This neither gave them control of the Goths nor protection against the armies that followed them. The Germanic tribes had their own social structures and no loyalty to the Roman state and would ultimately set up their own kingdoms within the empire. The massive expansion of the Roman empire led to an over-reliance on foreign troops to police their borders. Attempts to incorporate invading foreign troops into the military did not work and helped create many new kingdoms across Europe.
The Eastern Roman Empire would have had many of the same problems as the West in the 4th and 5th centuries. Their military was weak and overstretched, and the Gothic defeat of the Romans at Adrianople happened on their lands. The Eastern Empire did not fall however but became the medieval Byzantine Empire. The dangers presented by a weakened and overstretched military were not inevitable. The Byzantines would purge their armies of Germanic tribes under Leo I (457-474). The Greek East had a stronger economy and made better use of diplomacy to come to good terms with the invaders. These were important factors that could have prevented the fall of the West. Military problems did not prevent the survival of the Greek East. The problems in the Roman army were not the inevitable cause of the fall of Rome.
[P1] The huge size of the empire created a massive, hard to defend border [P2] The army was a huge financial strain on the Empire during Late Antiquity [P3] A lack of recruits would cause Emperors to recruit the very barbarians who caused Rome to collapse [C] A weak and overstretched army led to the use of unruly barbarian tribes including those who would later sack Rome
Rejecting the premises