The Emancipation Proclamation of 1863, an executive order issued by President Lincoln declared the freedom of slaves in the Confederate States that were at war with the North. The Emancipation Proclamation did not make slavery illegal The Thirteenth Amendment of the United States Constitution officially banned slavery. On December 18, 1865, the amendment was adopted. It was the adoption of the Thirteenth Amendment on December 18, 1865 which made slavery illegal with the United States of America.
The Thirteenth Amendment of the Constitution of the United States of America reads as:
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.