Short answers, pulled from the story.
The term "White race" or "White people" entered the major European languages in the late seventeenth century. It originated with the racialization of slavery, specifically in the context of the Atlantic slave trade and the enslavement of indigenous peoples in the Spanish Empire.
In 1758, Carl Linnaeus proposed what he considered natural taxonomic categories of the human species, distinguishing Homo sapiens from Homo sapiens europaeus and adding four geographical subdivisions: white Europeans, red Americans, yellow Asians, and black Africans. Although he intended these as objective classifications, his descriptions included cultural patterns and derogatory stereotypes.
In 1923, in United States v. Bhagat Singh Thind, the Supreme Court ruled that people of Indian descent were not White men and thus not eligible for citizenship under the Immigration Act of 1790. The court adopted a "common-knowledge" standard for Whiteness rather than scientific evidence, which it found incoherent.
The one-drop rule was a colloquial term for laws passed by eighteen U.S. states between 1910 and 1931 that classified any person with any known Black African ancestry as Black. These laws were declared unconstitutional in 1967 when the Supreme Court ruled on anti-miscegenation laws in Loving v. Virginia.
According to a study on genetic ancestry, White Americans on average are 98.6% European, 0.2% African, and 0.2% Native American. According to the 23andMe database, up to 13% of self-identified White American Southerners have greater than 1% African ancestry.
Under the Royal Pragmatic of 1501 in Spain's American colonies, Black African, Indigenous, Jewish, or morisco ancestry formally excluded individuals from the "purity of blood" requirements for holding public office. These restrictions also applied in the military, some religious orders, colleges, and universities, producing a nearly all-White priesthood and professional class.