Fall of the Western Roman Empire
Underlying causes

When Gibbon published his landmark work, it quickly became the standard. Peter Brown has written that "Gibbon's work formed the peak of a century of scholarship which had been conducted in the belief that the study of the declining Roman Empire was also the study of the origins of modern Europe". Gibbon was the first to attempt an explanation of causes of a Fall of empire. Like other Enlightenment thinkers and British citizens of the age steeped in institutional anti-Catholicism, Gibbon held in contempt the Middle Ages as a priest-ridden, superstitious Dark Age. It was not until his own era, the "Age of Reason", with its emphasis on rational thought, it was believed, that human history could resume its progress.

He began an ongoing controversy about the role of Christianity, but he gave great weight to other causes of internal decline and to attacks from outside the Empire.

The story of its ruin is simple and obvious; and, instead of inquiring why the Roman empire was destroyed, we should rather be surprised that it had subsisted so long. The victorious legions, who, in distant wars, acquired the vices of strangers and mercenaries, first oppressed the freedom of the republic, and afterwards violated the majesty of the purple. The emperors, anxious for their personal safety and the public peace, were reduced to the base expedient of corrupting the discipline which rendered them alike formidable to their sovereign and to the enemy; the vigour of the military government was relaxed, and finally dissolved, by the partial institutions of Constantine; and the Roman world was overwhelmed by a deluge of Barbarians.

After a diligent inquiry, I can discern four principal causes of the ruin of Rome, which continued to operate in a period of more than a thousand years. I. The injuries of time and nature. II. The hostile attacks of the Barbarians and Christians. III. The use and abuse of the materials. And, IV. The domestic quarrels of the Romans.
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