according to rousseau, what is the relationship between inequality and decline or indeed, lack of an ethical or moral sense in modern society ?

THis is similar to your last question. I think you can add mans' inherent greed. The arbitrary drawing of boarders, land rights and ownership inherently enslaves one man to another. The development of institutionalized inequality is a series of tricks played by the powerful on the weak, and so too is the ultimate foundation of civil society. This quotation emphasizes the extraordinary nature of the creation of property. It is after a strange act, which necessitates a supply of gullible people to witness it. Rousseau is very clear that the link between property and inequality is a direct one. Once property has been created, institutional structures emerge to fix it in place, and mankind is then "lost." Wars and conflict result from property because, as Locke says, "without property there is no injury." However, just as human development is irreversible, Rousseau sees no real way to return to a state in which the Earth was "no-one's." It was Marx's insight that only the abolition of property could resolve this situation.