That is one possibility.
Another possibility is that the alien civilization is like an intelligent insect hive... highly cooperative internally but ruthless toward any outsiders.
It doesn't seem likely that a civilization with a "hive mind" would engage in interstellar traveling. A civilization with hive mentalities would most likely stall at a Type I civilization (which is not enough for interstellar travel). Why do I think this? Well, let's take some examples on our own planet: Ants have remained in the same basic shape during a period where most mammals, birds, fish and dinosaurs managed to evolve into everything from pack hunters to omnivores to carnivores and went extinct. Think of it this way: In the period where some dinosaurs transitioned into birds, ants changed in minute ways. So how would this translate into a larger/more intelligent species? Pretty much the same. You'd have a civilization that is practically unchanged and so focused on the survival of the species that a sizeable risk like interstellar travel would be borderline unthinkable.
First, you have the issue of what
colonization or even
attacking another civilization actually entails from a social perspective. A species that is sending out a colonizing/attacking force
needs to be developed to the point where it can send a sizeable and expandable force. It needs to have resources to spare as well as well as population to spare. It would also need to have a defined social structure, system of writing and be either a type II or III civilization. It needs to have knowledge of mathematics as well as
some sense of aesthetics. These are all qualities which take tens of thousands of years to develop.
Then (for them to be of a hive mind) individuals within the society need to have developed to the point where all the things which come attached with an advanced social structure and knowledge of mathematics have been discarded/ignored or skipped altogether. So you'd have a civilization that somehow gained the mathematical knowledge as well as social development to achieve interstellar travel and then skipped/ignored/discarded aesthetics, arts, economics, philosophy and religion. Does that sound likely? That a species achieved interstellar travel but is somehow immune to
all of the little nuances which have existed in
every civilization we know of? Of course not. So we can immediately discard the idea that a "hive mind" species colonizing the universe is likely.
Then, you have the "life" issue. It's pretty well established that species with any sort of intelligence tend to be restricted by finite lifetimes. Whether this is based on the observation of creatures from our planet or not, there is only so long a creature can live and/or be kept alive. Is it possible to keep a being alive for 10,000 years of interstellar travel? Doubtful. Tissue degradation, contamination, illness, ship maintenance, all would have to be taken into consideration. You'd need a small force just to keep the ships maintained for the immense amount of time it takes to get from one star to another. Then you'd need substinance and whatever gas they breathe in ample supply for that force. So
just keeping a supporting cast through the trip would take immense amounts of resources.
In conclusion, not only is a colonizing group of aliens an
unlikely possibility, it seems illogical for a civilization to spend resources on a trip that may result in the decimation of a percentage of its population as well as the loss of resources. I'm looking at this from a realistic perspective, not a sci-fi perspective.
