President Lincoln understood that the Emancipation Proclamation was a wartime measure that would not ensure freedom after the war. He also knew that the slave states that remained loyal to the Union were not included in the proclamation. The only way to truly eliminate the institution of slavery was an amendment to the United States Constitution, which Lincoln successfully lobbied the U.S. Congress to adopt. Witnessed by jubilant African Americans seated in the galleries, the Thirteenth Amendment was passed by the House of Representatives by a vote of 119 to 56 on January 31, 1865. Secretary of State William H. Seward issued a statement verifying the ratification of the amendment by the states on December 18, 1865.