Gbaba

The Gbaba were an aggressive alien race that settled in roughly the same area as the Terran Federation. Their massive war against the Federation almost led to the destruction of the human race, and was the reason for the secret colonization of the planet Safehold.

History
The Gbaba developed on an unknown world somewhere beyond human territory, and achieved spaceflight long before humanity did.

At the beginning of the war, it seemed like the human race could gain victory due to their greater tactical flexibility. But then, the Gbaba showed their true strength: the entire fleet of the Gbaba empire appeared first in the Starfall System. Humans had nothing to counter the superior number of the Gbaba-owned starships, but despite that they defended their worlds until death.

A surprising fact, which was exposed during research on the Gbaba, was that some of their starships were several thousand years old, but were completely like their newest ships. This indicated that the Gbaba ships were not modernized or technically improved for an incredibly long space of time, suggesting that their culture had no inherent desire to progress. Because of that, some people -- like Admiral Pei Kau-zhi -- suspected that the Gbaba weren't even rational beings anymore and that it was quite possible they only acted by instinct.