The correct answer is the 14th amendment.
The 14th amendment was a constitutional amendment added in 1868 that stated that all individuals born on American soil are granted citizenship. This means that African-Americans who were formerly slaves now have citizenship. This also means that African-Americans have the same rights and protections as white citizens.
This overturns the Dred Scott case that stated that slaves were property and also invalidates black codes, as these laws unfairly limited the rights of African-American citizens.