It's not confederate because the confederacy in America promoted black slavery and the philosophes were against slavery and serfdom.
It's not monarchy because in a monarchy it's ruled by an absolute monarch which people don't have much control over, but it's different with an absolute monarchy because there are three branches of power like there is in America and Britain.
It's republic because its a type of ruling of democracy and a bunch of philosophes promoted a republic since as it could help the human society.
