It is entirely possible to conquer the known world, and it has happened. The Akkadians did it. The Sumerians did it. The Persians did it. The Greeks did it. The Romans did it. The Aztecs did it.The Mongols did it. You might say that they never conquered everything, but they conquered everything they knew existed and they're sphere of influence not only reached the known world, but dominated it. It's unlikely that on super-empire will rise and take over every country and landmass, but that's irrelevant to the question is it POSSIBLE.
This is where Pangea comes in to place.
It would be hard to rule the world if all the countries were split off.
In about 2 MILLION years, it might be possible because all the countries would be together from the idea of scientists.
But I don't know how they would choose.
They proably couldn't even pick a guy to rule the world either