The first truly modern element within modern political philosophy was the proto-liberalism that emerged during the eighteenth century. What was different about it as a view of politics was its insistence that certain universal political rights a) existed, and b) were conferred regardless of social status.
Along with this went a new view of economics, based on the idea that self-interest (selfishness) could be a positive factor in human affairs, and not simply a vice. This was a very great step, and one that many on the political right, especially in America, are completely blind to. Such people feel that individualism, with its concomitant political and economic privileges, is completely natural. It isn’t, as the entire previous history of the world can testify.
Where this new doctrine came from is a long story and one that is not entirely clear. But a combination of Protestantism and the sceptical rejection of religious dogma both had a role in its development.
Once liberalism had appeared, much else followed very swiftly. Hard on its heels, and from the same intellectual quarter, came socialism and nationalism, both also based on individual rights. These two – socialism based in economics and nationalism based in essences – became the two most influential collective philosophies of the last two centuries, and the most lethal. Both entirely changed, shaped and remodelled our collective thinking, along lines of class and kin/nation. Once these two genies were out of their bottles, a vast range of new possibilities opened up.
The grim consequences were reaped by the unfortunate great-great-grandchildren of the revolutionaries of the eighteenth century.