people created the ideas of countries, then made a list of them. USA is on that list.

People? Which people? If I get a bunch of people and declare a micronation within what the US considers it's borders, is that objectively a country or not? Or suppose I convince a bunch of Americans that Germany isn't really a country, does it then cease to be a country despite what the Germans themselves believe?

In any case, I would think that if something falls under the standard of, "This is true because a bunch of people say it is, even though there's nothing physical you can point to to prove it" then it seems somewhat absurd to call that an "objective fact" What do "objective" and "subjective" even mean, then?