As the title of the book suggests, A World Lit Only By Fire portrays the Middle Ages as a barbaric and brutal period of history.
For Manchester, this was an era dominated by chaos, violence and stagnation. At the heart of Manchester's thesis is the centrality of the Church. This was a powerful and pervasive organisation, plagued by immorality and corruption. It failed to provide proper leadership for the people of Medieval Europe and was also responsible for halting scientific advancement.
In essence, Manchester believed that this period deserved to be known as the 'Dark Ages'.