>>96285509
A single guy can't do it no matter who he is. It's a gigantic logistical undertaking. Just gathering the resources required just to figure out HOW to do it would take the poor guy over a thousand years. But if you have the manpower it's very much possible no matter how retarded everyone involved may be through sheer trial and error.

So really it boils down to if the space marine can conquer the world, which I personally find to be very dubious considering how little achieving that kind of power has with any kind of personal merit. And marines aren't even all that mighty individually!