Source: The Publisher Website.
There will be a time for peace in the galaxy, where life-forms can skip through the fields and read poetry, unworried by the threat of war, but this is not that time. There will be a time for song, time for cakes, time for long afternoon strolls, but this is not that time. There will be time for love, time for joy, time for writing that novel you know you have in you somewhere, but this is still not that time.
This is a time for war. Huge war, galaxy-spanning war, where the cries for mercy from the citizens of captured worlds will reverberate around the bridge of your flagship. A time for honor, for glory, for huge profits for people in the defense industry. This is a time for galactic conquest.
Galactic conquest is the campaign meta-game add-on for gratuitous space battles. The campaign 'wraps-around' the battles, so they are no longer isolated clashes, but merely engagements in an ongoing galaxy-conquering campaign. When you decide to move one of your space fleets to an enemy-controlled planet, a normal GSB battle takes place, and the winner takes control of that system. This radically changes the tactics of the game. No longer can you design ships specifically to fight a single enemy fleet, but you are forced to think ahead, to design multi-role ships and fleets that can take on all comers.
The galaxy you fight over has 52 different planets, with you in control of just one of them at the start of the campaign. You can play as any race from Gratuitous Space Battles, or it's expansion packs, and in your attempt to conquer the galaxy you will come up against enemy fleets from all the different races, including expansion pack races (if installed). The fleets you encounter will not be AI - designed, but they are the creations of other GSB players. In a cunning 'massively-singleplayer' system, GC will constantly download the fleet and ship designs of other players to fight as your opponents, whilst uploading some of your fleets to fight against everyone else. This way you will be constantly challenged and surprised by enemy tactics and ship designs.
Galactic Conquest requires that you have the base game (Gratuitous Space Battles) already. You can have as many or as few race expansion packs installed as you like, the campaign will pick enemy races based on which races are already installed. You will also NEED an internet connection as you play the campaign, because of the games tight integration with the online server that selects enemies for you to fight.