Why did the Roman Empire fall?

Rome's fall resists a single tidy cause, which is exactly why historians have debated it for centuries and produced a small library of theories. The traditional marker is 476 AD, when a Germanic leader deposed the last emperor of the Western Roman Empire, but that was the final push on a structure already crumbling from many directions at once. The leading factors, working together over decades: sustained pressure and invasions from Germanic and other groups along overstretched borders, an economy strained by heavy military costs, debased currency, and reliance on slave labor, chronic political instability with emperors murdered and armies proclaiming their own, an empire simply too vast to defend and administer, and dependence on foreign soldiers whose loyalty was uncertain. Older theories blamed moral decay or even lead poisoning; most modern historians favor the combination of military, economic, and political stresses.

The essential correction to the popular story is that Rome did not simply vanish in 476. The empire had split into western and eastern halves, and while the West fragmented into successor kingdoms, the Eastern Roman Empire, centered on Constantinople and known to historians as the Byzantine Empire, continued for nearly another thousand years, only falling to the Ottoman Turks in 1453. Its people called themselves Romans the entire time. So Rome fell gradually and unevenly, in the West through a slow-motion collapse of many overlapping failures, and in the East not until the middle of the 15th century, long after most people imagine togas and gladiators had ended.