// smuglord
We already have alien bacteria coming in to the earth from meteoroids
// smuglord
There is a rather large possibility that evolution went a drastically different way on the respective aliens' planet(s), meaning that the "implanted" genetic functions of their minds could be entirely different. Perhaps there were circumstances in their world that made working together, for some reason or another, unbeneficial, or any sort of factor in their history really, all of this most likely points to that their society would look a whole lot different from ours. (in addition that the will to power might not even exist in their minds)
This could mean that they're either huge assholes (from the perspective of humans), huge hippies, or have and orange-blue morality (obscure morality) - if we don't have data on how exactly their societies function, what their values are, it's going to be a bit presumptuous to assume that they're all imperialists. (Does that concept even exist for the said aliens?)
I wouldn't be surprised if several alien societies have a very similar structure as human society, but even in human society itself there are huge differences. (the Eskimos, for example, couldn't understand the concept of "war" when it was first declared on them)