That, too...
Heinlein explained that one definition of a weapon (as a class) is that of an engine to harness energy against an opponent. He who has the Moon, for example, once established, has enormous energy of position.
Whomever controls the High Ground controls the Earth. Anyone who develops the capability of controlling the Solar orbit of a substantial sized asteroid also develops the capability to destroy all human civilization on the Earth by causing the asteroid to collide with the Earth.