How did Islam develop in Arabia, and how did its followers create a vast empire so quickly?

I'm not convinced that this offers the best explanation for the military success of the Arabs. For one, we have very little idea of what tactics and equipment were used in the early battles thanks to the paucity of sources (the same goes for every other aspect of the seventh century as well). Secondly, the Romans and the Persians had to deal with Arab raids by centuries by this point and had at least developed a relatively reasonable way to deal with it - paying other Arabs living in the borderlands to patrol the frontier and to fight off raiders if necessary. It would be these auxiliaries that the first Arab forces would have fought, not Roman or Persian field armies, so to what extent were early Arab armies successful because of their nomad heritage, when they were fighting enemies with similar experiences?

Moreover, these imperial confederates had frequently turned on their imperial masters and were used directly in wars between the great powers, even in regions as far away as the Caucasian Mountains, so imperial troops had some experience of fighting Arabs already. The Strategikon (a Roman military handbook) from the late sixth century tells us that the Romans had certain strategies that they used against the Slavs, Avars and the Persians - why not against the Arabs as well? The Romans and the Persians were not arch-conservatives unable to deal with a new situation. They did have experience of fighting nomads (indeed, all their major foes in this period were nomads, such as the Avars, the Turks and the Hephthalites), and we have plenty of records indicating that they had excellent cavalry too, particularly the Persians.

I also think that you emphasised the superiority of Arab cavalry a bit too much. Not all Arabs were nomads. Islam was for instance born in the urban communities of Mecca and Medina, and Yemen too was relatively urbanised. Those living on the edges of the two great empires also had their own settlements or were at least familiar with them; the Lakhmids had the town of Hira, whilst the Ghassanids were lavish patrons of churches. Nomadic Arabs did take part in the conquests, but we should not attribute all of its successes to them alone. At the very least, I think a large chunk of the armies from Arabia, if not the majority, would have been made up of infantry and they played an important role in actually seizing new territories for the developing Caliphate.

/r/AskHistorians Thread