Civilization and nature
According to Freud, civilization is our defense against nature. This means that nature consists of basic violent and wild contrasts that civilization tries to control. It tries, as much as possible, to canalize such natural powers and to anthropomorphize nature.
Obviously this is possible with some limitations, since nature it is not fully controllable. All the same everybody that lives in a civilized country sees how life can be regulated by coexistence rules and can be pacific. He sees this daily and doesn’t need any demonstration of it.
Nevertheless the cultures are changeable; they born develop and die such as humans, since they are organisms that follow their own internal laws. The external environment can affect the enforcement of such laws but it cannot delete the laws themselves. At the beginning and until its climax each culture conquers some autonomy, i.e. some humanity and some freedom from the incoercible violent and irrational nature.
It is like an oil stain on the sea waves. But during their decline cultures loose such autonomy and the humanity is crushed by the wild nature and it is reduced to it; humans come back to nature without any distinction from it, back to the uncivilized stage.