In http://www.straightdope.com/classics/a5_248.html
Unca Cece, explaining how and why Christianity became so popular, sez:
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What set Christianity apart was its sophistication. It was the West’s first modern religion, coupling a coherent and attractive picture of how the world worked with a commonsensical moral code. Most western religions prior to Christianity, Judaism included, were narrowly focused ethnic affairs, primarily concerned with placating a perpetually pissed-off godhead. (The Roman state religion was merely an amalgamation of such local beliefs.) Christianity, in brilliant contrast, offered the following propositions: God is good, God is universal, God wants you to live forever with him in paradise provided you … well, exactly what you had to do to be saved was a matter of dispute. But the point was you could be saved…
The idea of salvation was appealing enough in its own right but it had an equally appealing subtext: the universe makes sense, you have a central place in it, and you can, up to a point, control your own fate. (I realize we get into the free will vs. predestination argument here, but you see what I’m getting at.) The complexity and emotional power of this system of belief swept away the primitive religions that preceded it. Tellingly, Christianity made less headway against the religions of the east, which offered a world view that was equally compelling.
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Fair enough. But then why did Islam, which came along a good five or six centuries later, make so much headway against these same religions? Pakistan, Bangladesh, Indonesia – all had been Buddhist, Hindi or both, but today are the largest Muslim states in the world. Islam has also swept North and East Africa, places where early Christianity made some intial forays, but never really took hold.
I am NOT interested in starting a religious war here, or debating which of these several religions is “better,” “greater,” “stronger,” etc. I’m looking for historical and/or cultural reasons why some faiths spread the way they did. Thanks.