The Dark Ages as they were referred to in many historical texts talk about and go into detail why that period of man were deep in superstition and religious wars or crusades and many of the deadly diseases that could have ultimately destroyed humanity but, the disease was known as the Black Plague due to a specific breed of rats that spread it around Europe and the United Kingdom with bites, scratches and people who ate them due to poverty and etc. Martin Luther in the time of the dark ages had written texts to reform the churchs and led to the Protestant Revolution. If you are looking to expand on this you can find many historical texts that go into specific parts or reasons the Dark Ages happened.
