Civilisation is the blossoming then shriveling of human understanding, manifested as the rise and fall of a dominant society.
A Dominant Society imposes its beliefs upon all other societies by violence (war) or its threat, which must involve the threat, or use of, genocide so any society that recoils from inflicting genocide will suffer genocide.
A Society is a shared understanding; a creature that has a life-cycle like any other as it first waxes to a prime under the influence of a majority of unselfish citizens that:
Before waning under the influence of a majority of selfish citizens who demand:
N.B. As a civilisation is a society, and a society is an understanding, then the study of civilisation must be the study of understanding, which is the realm of philosophy.