Persistent military pressure from barbarian tribes and the Empire's overstretched borders drained resources and manpower.

The Roman Empire's vast frontiers became increasingly difficult and expensive to defend. Waves of Germanic tribes, such as the Goths and Vandals, pushed into Roman territory, often provoked by the Huns, leading to major defeats like Adrianople (378 CE) and the Sacks of Rome (410 CE, 455 CE).