Because a vote can change who get elected
Britain viewed the Declaration of Independence as an act of treason, so they were all traitors. Some of the signers were captured by the British and executed for treason, and others had their homes ransacked and/or burned, the others died fighting.
13th Amendment
Section 1. 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.
Section 2. Congress shall have power to enforce this article by appropriate legislation.
