^Don't forget that Dark Mirror
says that the Terran Empire conquered their entire Milky Way Galaxy. How does that make any sense? They're never said to have any quantum slipstream drive, coaxial warp drive, jaunt drive, transwarp conduits, subspace tunnels, or anything that would conveniently allow them transportation throughout the galaxy. And how could they conquer everyone in two completely unexplored quadrants in a matter of only one century?