Zardnaar
Legend
If you are going to have The Evil One leading an Empire of Evil, it has to be dark there, and its reputation must have spread. The Empire need not - probably should not* - be "everywhere known".
In my campaign world, the metaplot is often 'pushing back against the Darkness, making bigger (or new) places for Light'.
* despite the success of the original Star Wars trilogy
If evil is everywhere (or functionally everywhere) the campaign can work it just changes tone (assuming the PCs want to oppose it). Darksun is like this I suppose.