The Thirteenth Amendment to the U.S. Constitution legally ended slavery in the United States. The Thirteenth Amendment was passed by Congress and ratified by the required three-fourths of the states in 1865. President Abraham Lincoln had issued the Emancipation Proclamation in 1862, declaring slaves in areas in rebellion against the government to be freed by executive decree. Afterward, Lincoln and many of his fellow Republicans had believed that more permanent legislation in the form of a constitutional amendment prohibiting slavery would be needed to ensure that the Emancipation Proclamation could not be subsequently ruled either unconstitutional or a temporary war measure.