The fall Roman Empire was abandonment of basic Judeo-Christian morality and lead to the Dark Ages and chaos. It is largely the same thing occurring in this nation. It was emergence of the church that put the pieces back together.
http://www.gotquestions.org/dark-ages.html
During this time it was the priests and the monks that saved from the ruins of the Roman Empire the treasures of classical literature—along with the Holy Scriptures and patristic writings—and preserved them for the future.
Dark, though, compared to what? The savagery Aztec culture, where strangers were captured and their hearts were ripped out while they were still alive? The cannibalism and backwardness of Indians on this continent? Has any Islamic culture every been anything but backward and totalitarian? Even during the Dark Ages, Western Civilization was superior to the rest of the world.
But it really was not until American and the separation of religion from government's control with both getting equal play in society that the true wonders occurred.