There are adherents to single factors, but more people think a combination of such factors as Christianity, decadence, lead, monetary trouble, and military problems caused the Fall of Rome. Imperial incompetence and chance could be added to the list. 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 A.D. 1453.
Theories on the Fall of Rome University of Texas: "210 Reasons for the decline of the Roman Empire." Source: A. Demandt, Der Fall Roms (1984) The first major historian to deal with the decline and Fall of Rome was the 5th century historian Zosimus, but the best-known name connected with the Fall of Rome is Edward Gibbon. Historians of ancient Rome have long been fascinated with the fall of this powerful empire.