It's history of immigration laws prior to the mid 20th century
The Naturalization Act of 1790 (1 Stat. 103, enacted March 26, 1790) was a law of the United States Congress that set the first uniform rules for the granting of United States citizenship by naturalization. The law limited naturalization to "free White person(s) ... of good character", thus excluding Native Americans, indentured servants, slaves, free black people and later Asians, although free black people were allowed citizenship at the state level in a number of states.
Your claim, so what’s the proof?
It's history of immigration laws prior to the mid 20th century
https://en.wikipedia.org/wiki/Naturalization_Act_of_1790