The aliens in Cixin Liu's books don't blow each other up because they're trying to expand. They do it because there's no defense against getting blown up, so th

The aliens in Cixin Liu's books don't blow each other up because they're trying to expand. They do it because there's no defense against getting blown up, so the only safe option is to blow up the other guys as soon as you detect them. There's no possibility of a tit-for-tat if you're dead as soon as the other side defects. I once read an article that calculated how much warning we'd have, if we could detect an incoming projectile at the edge of the solar system, and it were approaching the Earth at .99c. Since it would be traveling just behind the light we see from it, the answer was eight seconds. Cixin Liu might have a point.