No passing grade for you. Try again.
You're probably thinking of the 14th Amendment, created to give blacks the right to vote and to tie up loose ends in the Reconstruction as electors, un-Reconstructed rebels, Civil War debt, etc.
Previously to that, the U.S. followed jus soli rule of law which places citizenship upon place of birth, hence the "No Person except a natural born Citizen, or a Citizen of the United States, at the time of the Adoption of this Constitution, shall be eligible to the Office of President" clause of qualifications for President.
Someone born in New York in 1790 was a US Citizen by the legal tradition that birth determined citizenship. That is the understood legal foundation. The Constitution implicitly recognized two modes for citizenship - jus soli and naturalization, Article I, Section 8. Later amendments modified and spelled out aspects, including a limited jus sanguinis of those born to American citizens living abroad.
"The Constitution of the United States does not declare who are and who are not citizens, nor does it attempt to describe the constituent elements of citizenship; it leaves that quality where it found it, resting on the fact of home birth and upon the laws of the several States." opinion of the US Attorney General, 1862, quoted in A Treatise on American Citizenship, John Wise, 1906.