Consider this candid assessment of the Great historian, from the Hysterical History Hypocrites at Wikipedia (the world's "Encyclopeadia of Record") :
Gibbon offers an explanation for why the Roman Empire fell, a task made difficult by a lack of comprehensive written sources, though he was not the only historian to tackle the subject.
According to Gibbon, the Roman Empire succumbed to barbarian invasions in large part due to the gradual loss of civic virtue among its citizens. They had become weak, outsourcing their duties to defend their Empire to barbarian mercenaries, who then became so numerous and ingrained that they were able to take over the Empire. Romans, he believed, had become effeminate, unwilling to live a tougher, "manly" military lifestyle. In addition, Gibbon argued that Christianity created a belief that a better life existed after death, which fostered an indifference to the present among Roman citizens, thus sapping their desire to sacrifice for the Empire. He also believed its comparative pacifism tended to hamper the traditional Roman martial spirit. Finally, like other Enlightenment thinkers, Gibbon held in contempt the Middle Ages as a priest-ridden, superstitious, dark age. It was not until his own age of reason and rational thought, it was believed, that human history could resume its progress.