[Question] Why has no person /​ group ever taken over the world?

I’m actually kind of surprised at this, now that I think of it. Clearly there have been numerous people who have wanted to take over the world, and there have been several individuals or empires that have taken over significant fractions of the world. Are there any careful systematic studies that try to explain why no individual or group has ever (yet) succeeded? Is there some set of general theories that even attempts to explain this, in part or in whole, in a systematic way?

I feel like such a study might be quite valuable for a lot of different reasons, in addition to being interesting in it’s own right.