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

Talking about the development of Islam in Arabia is tricky, since we basically only have two vaguely contemporary sources - the Qur'an, which is a collection of Muhammad's teachings and seems to have been written down and compiled by the 640s, and the Constitution of Medina, a set of rules governing Muhammad's fledgling community in Medina that is preserved in a late eighth-century biography of the Prophet (but is probably from much earlier due to its archaic Arabic). What do the two sources tell us? Not very much I'm afraid. Muhammad definitely preached for a religious movement against the status quo, one that made some people (presumably at Mecca) angry and this led to some attacks on he and his followers. Then there was a migration of some sort to Medina, one which led to further fighting both internal and external between Muhammad's group and their enemies.

This might be surprising, but the Qur'an is actually pretty bad at giving us narrative details. There are very few mentions of Muhammad and geography, so this vague picture is the best we can extract from the Qur'an. For all the other details of Muhammad's career at this time we would have to rely on later sources, particularly from the Sira of Ibn Ishaq in the late eighth century, which only survives in an edited form by Ibn Hisham and al-Tabari from the ninth century. I don't think there is any reason to question the general framework of the story - that Muhammad fled from Mecca to Medina and then fought to impose his rule on both his home town and on the wider world. But the details, such as the precise details about who did what to whom and the motivations behind their actions? I'm not so sure. Oral history is a fantastic resource, but we have to be careful about trusting it implicitly. Even contemporary sources are terrible at recording what actually happened, so we need to treat them the same way. It is possible for instance to make the case that the general gist of the story from the Qur'an was expanded in later centuries by writers writing in a very different context, who were unfamiliar with the seventh-century world and thus left an imprint of their ninth-century mindset in their texts.

This is probably the best we can do for now, though if you are interested in further details the New Cambridge History of Islam (2010) has a very good chapter on this. Take a look too at Michael Cook's Muhammad (1983) for a basic introduction of the criticisms against the traditional narrative. As for the second part of the question, I think my answer linked by /u/farquier did a good job in pointing out the problems historians have with writing about this period. Nonetheless, I did attempt to explain how the Arab Conquests happened and why it was successful, though of course I am always open to further questions and suggestions from others :)

/r/AskHistorians Thread