The Naturalization Act of 1790 declared that citizenship could be granted to quote any alien being a free white person. After the 13th Amendment banned slavery, the right to become a naturalized citizen got extended to people of African descent. The much more desirable path to citizenship was whiteness. So you saw more and more people arguing their whiteness before state courts as judges made those haphazard rulings on who to let into the club.
The story of Bhagat Singh Thind, and also of Takao Ozawa – Asian immigrants who, in the 1920s, sought to convince the U.S. Supreme Court that they were white in order to gain American citizenship. Thind’s “bargain with white supremacy,” and the deeply revealing results.