The Caucasus or Caucasia is a region spanning Eastern Europe and Western Asia, situated between the Black Sea and the Caspian Sea.
Why are all white people called “Caucasians?” I don’t even need to do any research to confidently say that the majority of white people on the planet have no affiliation or heritage links with that place whatsoever.
Granted there is an alternate definition for the word “caucus” which is a political word originating in the United states in the 1700s by white men in political gathering discussion groups, so perhaps that’s how it got started. https://en.m.wikipedia.org/wiki/Caucus
“Caucasian” came from 19th century race “science”, along with “mongoloid” and “negroid.” You’re better better off not using it and not taking it seriously when someone else does.