> It begins with by questioning "why did Rousseau wrote about inequality if 100 years before no one in western culture cared about it"? Then he goes to show how the themes of liberty and social equality came from Canadian First Nations criticism of western culture

Well, La Boétie's "Discourse on Voluntary Servitude" dates back to 200 years before Rousseau, and I wouldn't say it was inspired by American Indians. I am not saying that the discovery and then the deep relations that France did have with American Indians did not play an important in the literature and reflections: on the contrary just a bit after La Boétie's time, Montaigne integrated them in his thinking. That was still over 150 years before Rousseau.

Edit: There were other major transformations at work, like the fact that before 1500, writers would either be lords or strongly depend on King or lords both for their income and for being allowed to publish. It was a Middle Age organisation, with a chivalry based nobility; writing essays was not a thing, the number of themes was as reduced as the number of forms. Then society organisation changed, bourgeoisie and nobles started mixing more and more; writing was more long-form (technical reasons come into play too) and of course expanded the number of themes it dealt with.