That they became predominant due to a culture of freedom and self-governance. They were fighting for hearth, home, and their own country, in a fundamentally different way than those fighting for an autocrat fight.
See Victor Davis Hanson’s Carnage and Culture, discussed briefly above. Strongly recommended reading.
Okay, that’s a valid criticism of his idea and worth discussing. He could say that that doesn’t necessarily apply to some of the Western European empires or come back with asking just why love of freedom develops in one part of the world rather than another. And you could say that he’s looking for material reasons, when the actual reasons might be intellectual or spiritual. And then you’ve got a real discussion going that takes you or the students some places they wouldn’t ordinarily go — which is part of what education is all about, isn’t it?