In GalCiv1 the Dreadlords, among other super-powerful races, would show up randomly. I believe they said they're going to add that into GalCiv2 at a later date. However, play through the Campaign if you want to see them now as it is story driven and deals with the Dreadlords.

i wish people would stop using moo2 to this game, they are not the same game and this is not a moo2 product.

In this case I think the parallel is justified. Not every point of comparison with Moo2 is arbitrary. The intro gives the impression that the Dreadlords will show up at some point, and in fact they do, just not in sandbox mode. It is perfectly understandable that the original poster could miss this.

A more general question on the whole 'super-powerful ancient races' theme, from someone who has not completed the campaign, is do we ever get to attempt diplomacy with these races or is military conflict the only possible outcome? I ask because inspiration for this part of the game seems to me traceable not so much to Moo2 as to Babylon 5, and a diplomatic solution was used in B5 by the younger races to the problem of vastly powerful ancient races (for Arnor and Dreadlords read Vorlons and Shadows).