Why do (mostly) americans use "caucasian" to describe a white person when a caucasian person is literally a person from the Caucasus region?

Sometimes when I say I'm Caucasian people think I'm just calling myself white and it's kinda awkward. I'm literally from the Caucasus 😭

(edit) it's especially funny to me since actual Caucasian people are seen as "dark" in Russia (among slavics), there's even a derogatory word for it (multiple even) and seeing the rest of the world refer to light, usually blue eyed, light haired people as "Caucasian" has me like.... "so what are we?"

p.s. not saying that all of Russia is racist towards every Caucasian person ever, the situation is a bit better nowadays, although the problem still exists.

Peace everyone!