Why did President Lincoln reverse General Fremont's order to liberate captured slaves?

President Abraham Lincoln reversed General John C. Fremont's order to emancipate (liberate) slaves in Missouri in 1861 for a variety of political and strategic reasons. Fremont, who was in command of the Department of the West, unilaterally issued a proclamation on August 30, 1861, which declared martial law in Missouri and freed the slaves of those in the state who were actively supporting the rebellion against the United States. This was an early and radical measure taken at a time when the official policy of the Union government had not yet fully committed to emancipation as a war aim.

Lincoln was concerned that Fremont's action could push the slaveholding border states that remained in the Union—such as Kentucky, Missouri, Maryland, and Delaware—towards siding with the Confederacy, as they were already sensitive to federal interference with their slave property. Lincoln was seeking to keep these states in the Union, viewing their support as strategically critical to the Northern war effort.

Furthermore, Lincoln worried that Fremont's proclamation could alienate conservative Northerners who might not be willing to support the war if they believed its purpose was to abolish slavery, rather than to preserve the Union. At the time, emancipation was still a controversial issue, and Lincoln felt that such decisions should be made at the federal level, not by individual generals.

As a result of these considerations, Lincoln asked Fremont to modify his order to conform with the federal government's position, which was not yet ready to enforce general emancipation. When Fremont refused to comply, Lincoln directly revoked the order and later removed Fremont from his command.