The 13th Amendment comprises a very short statement that prohibits slavery, except for convicted criminals, and a short statement that allows Congress to pass laws to enforce this prohibition:
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.
This amendment was first introduced in the U.S. Senate early in 1864, when the war was still under way. The Senate passed the amendment in April 1864, but the House did not pass it until January 1865. After Lincoln was assassinated in April 1865, his successor Andrew Johnson made ratification of the 13th Amendment a requirement for readmission to the Union. Eighteen states ratified it very shortly after Congress formally approved it. After much delay by the former Confederate states, it was ratified by the minimum of twenty-seven of the thirty-six states on December 6, 1865.
Texas did not formally ratify the 13th Amendment until February 18, 1870. Until then the official position in Texas was that this amendment already had been implicitly adopted. This position was adopted by the Constitutional Convention of 1866. As the Handbook of Texas explains, "[T]he members agreed that the Thirteenth Amendment, by then a part of the Constitution, had abolished slavery and that since they had taken the oath to support that Constitution, they had indirectly abolished slavery. They reasoned, therefore, that a direct and formal ratification of the amendment was not necessary and voted to allow the taking of the constitutional oath to suffice."