Wikipedia
Conquerors'
The Conquerors trilogy is a series of science fiction novels by Timothy Zahn, published between 1994 and 1996.
Set in a space opera future, the trilogy is concerned with a failed first contact that leads to an interstellar war between humanity and an alien race, the Zhirrzh (nicknamed by humans The Conquerors). Meanwhile, other alien races try to take advantage of the conflict between the two powers.