John Lord 
Beacon Lights of History, Volume 3 part 1: The Middle Ages [EPUB ebook] 

Beacon Lights of History is a 14-volume set first published in 1902. This collection of John Lord’s lectures spans 6, 000 years of European and American history. The first 12 volumes are all Lord’s work; the 13th was completed from his notes and the 14th is follow-ups by other authors.
The most extraordinary man who arose after the fall of the Roman Empire was doubtless Mohammed and his posthumous influence has been greater than that of any man since Christianity was declared, if we take into account the number of those who have received his doctrines. Even Christianity never had so rapid a spread. More than a sixth part of the human race are the professed followers of the Arabian prophet.
The question to be considered, then, is whether Mohammedanism spread in consequence of its truths or in consequence of its errors.