The correct answer is The 14th Amendment.
The Plessy vs. Ferguson case stated that all slaves were considered property, not people. This severely limited the rights of enslaved African-Americans during the mid 1800's. However, this all changed with the 14th amendment.
The 14th amendment grants citizenship to all individuals born on American soil. With citizenship comes all the rights outlined in the US Constitution. This includes the freedom of speech, religion, right to petition, etc.