The "Dark Age" is a myth created by Italian secular humanists and perpetuated by their fellow humanists throughout history. The more things change, the more they stay the same.
An alternative view: The "Dark Age"occurred owing to suppression of new ideas by the Church and Popes, and ended only when Martin Luther challenged the authority of the Vatican. Elements of the Dark Ages are perpetuated by their fellow fundamentalists who refused to accept the Germ Theory of Disease, refused to accept women as equal citizens, refuse to accept women as spirtual in leadership.
The US Constitution derives from the Enlightenment. It is not even a tiny bit Christian. It rejects all the previous church hierarchies and claims to 'truth' in matters of government.