Through 18th century, physical differences became an issue, eventually, skin color emerges as a way to divide. There may be reasons for minorities to maintain such beliefs as well.
Most minorities see a different picture.
Until about 1920, Irish, Germans, Poles, Italians, Russians, etc. were studied as separate races. Few now consider Italians, Irish, etc. as separate races, but do consider Africans, Asians as separate races. In this Christian country, Christian groups that are not mainline Protestant have had to assimilate with the dominant Protestant culture. Jews and Muslims have faced the same problem. What is the US way of life is still being formed.