There will be two new civilizations in Galactic Civilizations II (on top of the 8 from Galactic Civilizations: Altarian Prophecy).

The first one is called the Iconians.  The Iconians are the ones who actually created the Yor.  The Yor being a race of sentient machines.  The Iconians were once the servants of the dark Precursor race known as the Dreadlords. When the Dreadlords were gone, they considered themselves as the rightful heirs to the galaxy.  To that end, they built a race of machines to act as their slaves.  The Iconians possessed a great deal of Precursor technology but didn't fully understand it. This worked against them as they ultimately paid the price when the Yor turned against them and nearly wiped them out.  The Iconians fled to a distant corner of the galaxy where they slowly rebuilt.  Ironically, they independently had hyperdrive technology already but simply did not have the ability to exploit it until now.

The other race is the mysterious Thalan. They are an insect-like civilization with a centralized hive mind.  They are completely alien to us in how they work. Not much is known about them yet but we will fill you in as we learn about them.

In Galactic Civilizations I the races compete for their turf in the galaxy. In Altarian Prophecy the humans and Altarians learn much about each other and become allies. However, the real powers of the galaxy were the Drengin Empire and the Arceans. Humanity was left relatively free to expand into the galaxy because the Drengin were kept at bay by the Arceans.  But something has now happened. Something has given the Drengin an advantage and they are slowly wearing down the Arceans and the humans must now race to get friends and allies before the Drengin consolidate.  The problem being, there is something else out there lurking far worse. And don't count on the Drengin "teaming up" with the humans to battle it.  The Drengin Empire is evil. They're not misunderstood. They're evil. And through the course of the campaign it will become quite clear just how evil they are.

This is the part where we remind people that they will stil be able to play in sand box mode just like GalCiv 1. The campaign is there for those who are interested in playing out the story.  The story will be multi-dimensional (i.e. non-linear).