If group selection—the differential survival and reproduction of groups—is an evolutionarily stable strategy, then:
a) the characteristics of the group must be heritable
b) groups are only formed by related individuals
c) family members of groups behave altruistically to one another but not to unrelated members of the group
d) a small portion of the group must sacrifice their own fitness for the good of the group

you did not attach the discourse, but i assume it to be the discourse on the origin and basis of inequality among men (the original titile in french is: "discours sur l'origine et les fondements de l'inégalité parmi les hommes"), also know as "second discourse". in this discourse, jean-jacques rousseau emphasizes that private property is the basis of all inequalities.

therefore, what enabled the old regime to maintain as long as it did was private property.