More specifically, what formations and fighting styles did they utilized when facing the Byzantines and (to the great misfortune of all of humanity) defeating the Sassanids? Are there any books one could recommend on the subject?
Hi there,
The early Islamic conquests are fascinating, as you have an army with very mediocre equipment, fighting against supposedly superior forces and winning seemingly miraculous victories. Their fighting styles seemed to involve erecting barricades or using natural defensive positions, and fighting the battle around these barriers. This is discussed in John Keegan's History of Warfare, (1991) in the chapter dealing with motivations for fighting and religious fanaticism. Though a dated source at this point, it is an absolutely brilliant book on military history, and is worth reading to critique as well as to learn from.
Primary sources on the subject are harder to find, though I believe the Qu'ran itself has accounts of the very early battles involving Islamic armies. Though that is me attempting to remember as far back as my undergrad.