The "140" years comes from the time Constantine made Christianity the official religion of the Empire in the mid 330's to Rome's fall in 476. I won't solely blame Christianity for Rome's fall but it did play a part, Multiple civil wars between groups of Christians weakened Rome's central authority which made them more vulnerable to the Huns and Vandals. Also because the Visigoth's were willing to convert to Christianity the Romans allowed them to immigrate into their territory, A devastating mistake and one Battle of Adrianople and sack on Rome later the fall was inevitable.
A side note about Constantine: I find it very ironic that Christianity which is supposedly a pacifist religion and a religion of the poor gained prominence because a rich and powerful emperor saw a cloud in the sky and believed it was a sign from God to kill people. I guess he read too much of the Old Testament.
It appears most of your knowledge came from Gibbon. There are a lot of contested theories on this subject, and many contradict your (Gibbon's) theory blaming Christianity. You use Gibbon's date of 476; but the choice of that date was more arbitrary than factual considering the empire lasted another 200 years or so. Of course, some say it never fell since Rome is still there ... LOL.
A side note about Constantine: I find it very ironic that Christianity which is supposedly a pacifist religion and a religion of the poor gained prominence because a rich and powerful emperor saw a cloud in the sky and believed it was a sign from God to kill people. I guess he read too much of the Old Testament.
Christianity is not a pacifist religion. Jesus came not to send peace on earth, but a sword. And Christians resist the devil until he flees from them. I agree that God never intended for nations to be war-like for the sake of being war-like; nor did He intend for the slothful to benefit from the labors of others; nor perversion to become the norm rather than the exception. There is no doubt that many cults have arisen in Christianity that oppressed and suppressed (and no doubt a few in Rome, as in Europe); but there is no doubting the success of our Western Civilization.