Humans (Revelation Space)

The Revelation Space Universe concerns humanity's discovery of the Inhibitors, an ancient alien race, and their plan to annihilate the human race.

Humans have genetically modified either their own species, or species like dolphins, pigs and primates, to a human-like level of sapience.

Early in the 23rd century, they discovered a new method of near-light-speed interstellar propulsion called Lighthugger spacecraft. This led to decentralized interstellar settlement, where each planetary system colonized by humans is governed separately with their own politics, societies and economies.

Being a "young" star-faring civilization, they think about the Fermi paradox - 'where are all the aliens?'. Most civilizations found via interstellar colonization are long-dead, extinct, non-sapient flora and fauna, or highly alien lifeforms that are hard to specify. All that changed forever though in the Human-Inhibitor War which was a far-reaching conflict between the inhabitants of human-colonized systems and the onslaught of the Inhibitors after their ancient machinery was awakened as a result of tampering by the crew of lighthugger called Nostalgia for Infinity.

The Inhibitors were eventually stopped and defeated but at a great price.