In the movie, there's some dialogue between John Carter and Matai Shang, where the latter elaborates a little on the reasons they do what they do. I didn't get it, though. When asked by John Carter about their cause, he says they have none, but still for some reason have an agenda, and all their machinations, the wedding and giving the ninth ray to Sab Than, fits into it. Then he says:
We don't cause the destruction of a world, Captain Carter. We simply manage it, feed off it, if you like. But on every host planet, it always plays out exactly the same way. Populations rise, societies divide, wars spread. And all the while, the neglected planet slowly fades.
What does he mean with 'feed off it'? Seems like their motivations are to direct civilization in a way to minimize ecological damage?