As you grow confident by completing the Omega turn#700 game by absorbing all minor races through membership using diplomatic pressure, and also crushing opposition through military conquest of ships and ground invasions, then you are ready to start playing a game as a stronger opponent with an established empire than the other major races.
This saved game as the Omega turn# 400 has zero minor alien races, but 3 major opponent empires: Khaoran, Terrans, and Heyoun.
viewtopic.php?f=107&t=7712
You should be able to easily beat them as your counterintelligence ability exceeds theirs. They probably will join forces to oppose you by using sabotage.
This allows maximal colonization as the AI has plenty of open sectors to expand, with no competition from minor alien races, and so no need for them to conquer them. But eventually their borders will touch the borders of their neighbors...bringing collaboration and conflict.
What I did was ally with the Terrans and Heyoun, and was going to have a non-aggression pact with the Khaoran (they really are supposed to be honorable people, but also conquerors). But their goofy zealous low level raiders attacked Omega colonists killing billions. So that kind of bullying needs a vigorous calculated total response as bullies don't respect diplomacy.
So I clobbered them with sabotage. Then they kept attacking, so I annihilated their raiding. They kept attacking and I CRUSHED them. It set them back for 100 turns and only in turn #409 relented. They became the Omega's nemesis.
I don't blame them. War requires an enemy. It ain't personal. To a Khaoran, maybe such attention is almost friendly even romantic. The way alien species will think and what motivates them, is not going to be like a human. Their species is unique and their culture and society evolved based on a totally different history and the rigors of the climate and limited land mass and planet types in their homesectors. They will not have100% shared values with human beings nor the Omega. They may each have 0-100% shared values and the ones that do, like your empire more...
or fear or respect or even admire yours.
See BotE is a thinking person's strategy game. It's profoundly deep. It's a game for Irish warrior poets and samurai and philosophers.
https://en.m.wikipedia.org/wiki/Oisín