With an iron fist, they maintained a relative peace for Millennia, rulling the entire world and expanding their conquest." to
"Still hungry for expansion, the early V2 program evolved into immense war machines, and from these spaceships they colonised and ruled the galaxy.
With an iron fist, they maintained a relative peace for Millennia, further expanding their conquests to the entire galaxy.
It just sounds a bit better and makes more sense that way.