text: At the same time, Grant captured Vicksburg and gained control of the Mississippi River, splitting the far western rebel states.Emancipation Proclamation The Federal government's power to end slavery was limited by the Constitution, which before 1865 was understood to reserve the issue to the individual states.Lincoln believed that slavery would be rendered obsolete if its expansion into new territories were prevented, because these territories would be admitted to the Union as free states, and free states would come to outnumber slave states.He sought to persuade the states to agree to compensation for emancipating their slaves.Lincoln rejected Major General John C.Frémont's August 1861 emancipation attempt, as well as one by Major General David Hunter in May 1862, on the grounds that it was not within their power and might upset loyal border states enough for them to secede.In June 1862, Congress passed an act banning slavery on all federal territory, which Lincoln signed.In July, the Confiscation Act of 1862 was enacted, providing court procedures to free the slaves of those convicted of aiding the rebellion; Lincoln approved the bill despite his belief that it was unconstitutional.He felt such action could be taken only within the war powers of the commander-in-chief, which he planned to exercise.On July 22, 1862, Lincoln reviewed a draft of the Emancipation Proclamation with his cabinet.Peace Democrats (Copperheads) argued that emancipation was a stumbling block to peace and reunification, but Republican editor Horace Greeley of the New-York Tribune, in his public letter, "The Prayer of Twenty Millions", implored Lincoln to embrace emancipation.