There are adherents to single factors, but more people think Rome fell because of a combination of such factors as Christianity, decadence, and military problems. Even the rise of Islam is proposed as the reason for Rome's fall, by some who think the Fall of Rome happened at Constantinople in the 15th Century. Here I am writing about a roughly fifth century fall of Rome (or the western division of the Roman Empire).
1. ChristianityWhen the Roman Empire started, there was no such religion as Christianity, although by the time of the second emperor, Jesus had been executed for treasonous behavior. It took his followers a few centuries to gain enough clout that they were able to win over imperial support. This came in the early 4th century, with Constantine, who was actively involved in Christian policy-making. Over time, Church leaders became influential and took power away from the emperor; for example, the threat of withholding the sacraments compelled Emperor Theodosius to do the penance Bishop Ambrose required. Since Roman civic and religious life were the same -- priestesses controlled the fortune of Rome, prophetic books told leaders what they needed to win wars, emperors were deified, Christian religious beliefs and allegiances conflicted with the working of empire.
4. InflationRight now, the price of an ounce of gold is $1535.17/ounce (EUR 1035.25). If you bought what you thought was an ounce of gold and took it to an appraiser who told you it was worth only $30, you'd be upset and probably take action against the gold seller, but if your government issued money that was inflated to that degree you would no more have recourse than you'd have the money to buy necessities. That was what inflation was like in the century before Constantine. By the time of Claudius II Gothicus (268-270 A.D.) the amount of silver in a supposedly 100% silver denarius was only .02%.
- Poor management,
- The dole (bread and circuses), and
9. Want Even More?
The University of Texas has re-posted a German list ranging from the puzzling (like "useless eaters") to the obvious (like "stress") with a bunch of good ones in between (including "Nationalism of Rome's subjects" and "Lack of orderly imperial succession": "210 Reasons for the decline of the Roman Empire." Source: A. Demandt, Der Fall Roms (1984)
Do read the 21st century books The Fall of the Roman Empire: A New History of Rome and the Barbarians, by Peter Heather and The Fall of Rome and the End of Civilization, by Bryan Ward-Perkins, which are summarized, reviewed and compared in the following review article:
"The Return of the Fall of Rome
The Fall of the Roman Empire: A New History of Rome and the Barbarians by Peter Heather; The Fall of Rome and the End of Civilization by Bryan Ward-Perkins,"
Review by: Jeanne Rutenburg and Arthur M. Eckstein
The International History Review, Vol. 29, No. 1 (Mar., 2007), pp. 109-122.