I have recently heard two diametrically opposed versions of the Islamic conquests of Arabia and beyond. One claims that it was humane and entirely defensive (& without slavery)...the other that it was incredibly brutal. I have also heard that there is a great deal of revisionism on this issue. Can some one please give me a run down on what actually happened?
Hi, I can't speak about the conquests within Arabia, but since you mentioned 'beyond' as well, I think that my previous answers will be relevant here.
In this comment I outlined the basic issues with the evidence for early Islamic history and how modern historians see them. It is also worth commenting here that 'revisionism', in this context, is not a bad thing. Historians constantly revise their interpretations of the past and in an exciting field such as this, being a 'revisionist' is an entirely acceptable label. For the actual course of the conquests, I'm afraid I haven't mustered up the energy to write a detailed overview yet, but I covered it in more general terms in my answers on why the Arab conquests succeeded and how Christians reacted to it. Note that I'm also convinced that we can't be sure about 'what actually happened' yet, since there is still a great deal of material that we don't know or can only speculate about, particularly for the earlier period. This might be disappointing for you, but this is the position taken by many academic historians.
The seventh century was an exceedingly complex one and I think it is a disservice to the people of the time to describe the wars either as 'humane' or 'incredibly brutal'. In my answers I tried to outline this complexity, exploring both the peaceful surrenders and the brutal battles, but even then I don't think it is enough. Any narrative that explicitly favours one of these positions is ultimately incorrect, as they instead imposed their own judgement on the past rather than seeing it in its own terms (and thus perhaps more in dialogue with events in the modern day rather than what actually happened in the past). If you want to read a good book on this topic, consider Robert Hoyland's In God's Path: The Arab Conquests and the Creation of an Islamic Empire (2014) for an excellent historian's take on the conquests themselves, or Peter Sarris' Empires of Faith: The Fall of Rome to the Rise of Islam, 500-700 (2011) for a more general narrative of this entire period and for an understanding of its late-antique context.
I highly recommend the excellent series of posts by u/shlin28 in response to this question.
The gist is that a LOT of new and important scholarship is developing right now on the early Arab conquests and much of what we earlier assumed based on shoddy sources turns out to have no real basis to support it. I wouldn't call it "revisionism" so much as "exciting new research."
As for your two portrayals: both sound like inaccurate straw-men to me. The Arab conquest was neither defensive nor incredibly brutal. But seriously: read those posts I linked. They'll explain the current state of scholarship and our best interpretations of what happened and the controversies surrounding it much, much better than I possibly could.
Edit: Oops. Ninja'd by the author of said post. Oh well.