I agree that the US isn't a libertarian nation, but that's a question about the gulf between ideals and practice. That's also not the historical question I raised about the relation between libertarianism and classic liberalism.

But anyway, I've written a lot about economic inequality in developed nations, especially the US. Recently I've been focusing on religion and existential philosophy, but I've written series on conservatism for being little more than a series of excuses for social Darwinism, and on economics for likewise supplying propaganda for capitalist excesses.

The question that you raised here is narrower since it's about the origin of libertarianism. Regardless of its origin, the movement is certainly being used presently as phony populism. Libertarians say that grotesque inequalities are justified when they result from our free actions. This is just more social Darwinism, as I see it.

By the way, I have two long articles against Ayn Rand's libertarianism that will be coming out soon.