Democracy is premised, in some measure, on majority rule, and democracy is difficult in a situation of concentrated inequalities in which a large, impoverished majority confronts a small, wealthy oligarchy.
In the 19th century it was basically nationality and people trying to define their nationalism and create states which would reflect their nationalism. In the 20th century, ideology came to the fore, largely, but not exclusively, as a result of the Russian Revolution and we have fascism, communism and liberal democracy competing with each other. Well that's pretty much over.
Since the revolution of the 18th century, America has basically had an ideology of liberal democracy and constitutionalism.
Fascism and communism have not entirely disappeared but have been sidelined certainly, and liberal democracy has come to be accepted, in theory at least, around the world, if not always in practice.