The inerrant (and inherent) driving force behind human nature is selfishness, the need to survive, the need to pass on the genetic line, the satisfaction of basic human needs : shelter, food etc.
To this end even altruism is selfish, I can't kill a saber tooth tiger, but ten of us can and one tenth of the meat is better than none of it.
War, nationalism, patriotism, religion, tribalism, ethnic prejudice are all subversions and manipulations of this basic state of human nature to rise the few over the many, to ensure dominance of certain bloodlines and favourable genetic survival traits.