Let me add that demography is not always destiny, nor has it always been so. Western Europe from 800-1830 or so, was far inferior demographically to the various Caliphates, yet it pushed back on them, from Spain to finally, the Balkans.
Big populations have a weakness. They are constantly on edge of riots and revolt. China has been plagued with that, throughout its history, and so was the Roman Empire and many of the Caliphates. And because they are so big, they generate massive resistance to change. As Bernard Lewis has written, Muslim societies in Turkey, in Egypt, in Tunisia, in Morocco, and Persia, all tried to adopt and adapt Western technology, from the Printing Press to firearms, yet failed completely to produce any real competitiveness with Western technology. Science works the same for Muslims as Christians, the laws of physics don’t change for religion.
It was the population size that hampered them. Yes, human wave attacks can succeed if populations are too small, or disunited, or lose technological competitiveness. But the Crusader advantage in the Holy Land was technological. Far more heavily armored and armed knights would annihilate far less well armored and armed (but more mobile) Arab opponents. Yet the same basic technology of steel and iron was available to both cultures.
You can see this in business. Big corporations have so much entrenched interests that they routinely reject game-changing technology that threatens core businesses. Xerox with PARC and the fore-runner of the GUI computer system, KODAK with digital imaging, and so on.
