The 13th Amendment to the United States Constitution, ratified in 1865, abolished slavery. It states: "Neither slavery nor involuntary servitude, except as a punishment for crime whereof the party shall have been duly convicted, shall exist within the United States, or any place subject to their jurisdiction."
The other options mentioned relate to other amendments and legal principles. The 14th Amendment addresses citizenship and equal protection, while the 15th Amendment ensures the right to vote regardless of race. The phrase "ensure the blessings of liberty" is more generally associated with the preamble of the Constitution.