It's Voltaire (1694-1778). Depending how you count, The Enlightenment is or isn't part of modernity.
Did you think democracy was not a modern idea? It unequivocally is. The word comes from Ancient Greek, but what they did had almost nothing to do with the current definition of the word.
This focus on ethnic groups that you have is simply just not germane to this discussion. Democracy as it is currently understood does not have anything to do with "ethnic self-determination" (reeks of Blut und Boden - what the hell does it even mean to have an "ethnic self"?).
I don't know if you are inspired by neo-fascist thought or what's going on, but your understanding of democracy is extremely unconventional.
> reeks of Blut und Boden
Definitely linked to that sort of thinking. It sounds very inspired by 18th/19th century ideas of race (the ideas based on science that was debunked by the mid 20th century and has been thoroughly disproved by genetics).
The problem with these sorts of arguments is they take little bit of truth and some real examples (there are societies with politics is very tied into ethnic identities, there are groups defined by culture and language that want their own states) and treats them as the norm.
Find me one single definition of Modernity that excludes the 18th century.