In political science, the term ‘cleavages’ refers to social divisions which are sufficiently serious to form the basis of opposing collective identities and to give rise to organizations to promote or protect these collective interests.
Cleavage is not the same as conflict.
So, where there are significant cleavages there may be conflict, though this is not necessarily the case.
Rokkan Identified four major processes of historical transformation in western civilisation which, he argued, formed the bases of party systems across western Europe.
National revolutions which created unified states and broke up regional and local affiliations [Prussia, growth of modern Italy, France etc.]
The industrial revolution which replaced the local loyalties of agrarian society with economically specific groups of interests amongst classes (and was also partially responsible for declining religiousity)