how does Freud connect civilization with violence?

"For Freud, the greatest struggle in life is the connection between our inner world and the society into which we are born. Thus harmony and inner peace can only be attained when we have learned to control our aggressive impulses by resolving this incongruity. However, because Freud believed that destructive forces are present in all individuals, and thus man is by nature, an essentially anti-social and anti-cultural being, it is difficult for many people to accept his premises. After all, describing man as aggressive and out of control is hardly in line with humanity's superior self-image. Furthermore, while Freud's reference to aggression as "an original self-subsisting instinctual disposition in man . . . the greatest impediment to civilization" effectively defines the problem, he fails to offer legitimate solutions as to how to control our aggression and anti-social instinct."