1. Invasions by Barbarian tribes
The most straightforward theory for Western Rome’s collapse pins the fall on a string of military losses sustained against outside forces. Rome had tangled with Germanic tribes for centuries, but by the 300s “barbarian” groups like the Goths had encroached beyond the Empire’s borders. And with a weaker army it was easier for barbarian tribes to invade.
2. Overexpansion and military overspending
At its height, the Roman Empire stretched from the Atlantic Ocean all the way to the Euphrates River in the Middle East. Even with their excellent road systems, the Romans were unable to communicate quickly or effectively enough to manage their holdings. Rome struggled to marshal enough troops and resources to defend its frontiers from local rebellions and outside attacks.
