The word “Caucasian” was first used in 1795 by the German professor Johann Blumenbach to describe white people.
Although some genealogists today argue that modern Europeans trace their ancestry back to the Caucasus, this is not why Blumenbach chose this term. In his own words: “I have taken the name… from Mount Caucasus, both because its neighbourhood, and especially its southern slope, produces the most beautiful race of men”. He goes on to describe Caucasians as “colour white, cheeks rosy; hair brown or chestnut-coloured, head subglobular; face oval, straight its parts moderately defined, forehead smooth, nose narrow, slightly hooked, mouth small”. In other words, using the “most beautiful race of men” to describe white people was Blumenbach’s way of putting white people at the top of the racial hierarchy.
Using “Caucasian” for what he perceived as the physical ideal meant putting other races at the bottom, which was especially useful for Americans at the time who were searching for justifications for slavery. They incorporated that label into the US legal system and despite efforts to remove it from American lexicography, it’s still widely used to describe white Americans today.