As dave1949 notes, as a species we tend toward aggression, yet at the same time we are social beings. When you think about it, there are survival benefits in both traits that would bring them to the fore in natural selection. Where two tribes lived in enough close proximity so as to compete for resources, the more aggressive and/or intelligent group would "displace" the meeker one. We see this in much of nature where strength and aggressiveness is rewarded in breeding opportunities.
Being social has obvious advantages too, while living in groups offers protection, diversification of talents, a multiplication of knowledge and more, living in groups can conflict with aggressive behavior. And so, society has leaders, rules, etc.
It seems unlikely any successful, advanced civilization would be all that much different.