What empire fell and what empire caused it to fall?

Roman Empire

The Fall of the Western Roman Empire (also called Fall of the Roman Empire or Fall of Rome) was the process of decline in the Western Roman Empire in which the Empire failed to enforce its rule, and its vast territory was divided into several successor polities.

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