I see no way a species that can technologically spread to a couple of star systems would stop expanding. If you're scared of nasty aliens, the best defence is

I see no way a species that can technologically spread to a couple of star systems would stop expanding. If you're scared of nasty aliens, the best defence is to conquer the whole galaxy before them. There is no way to hide from an interstellar civilization. Nasty or not, they could always produce self replicating probes and keep track of the whole galaxy. Also, if you were able to colonize a couple of Star Systems, there's no way you are an anxious/scared species,