When did the Roman Army decline?

[Michael Kerr]

Would the fact that by Aetius's time he could not call for troops or military support from Eastern empire unlike Principate emperors who could transfer armies or units from east or west to converge on troublespots. May be Eastern Empire gave west covert support but it looked to me that they just sat out the conflict between Aetius & Attila as by this time they were 2 separate empires. With revenues cut by loss of Africa & Spain & no access to Eastern troops or reinforcements the western empire would have perpetual manpower problems.
Regards
Michael Kerr