The Slave Power (sometimes referred to as the "Slaveocracy") was a term used in the Northern United States (primarily in the period 1840–1875) to characterize the political power of the slaveholding class in the South.

The problem posed by slavery, according to many Northern politicians, was not so much the mistreatment of slaves (a theme that abolitionists emphasized), but rather the political threat to American republicanism, especially as embraced in Northern free states. The Free Soil Party first raised this warning in 1848, arguing that the annexation of Texas as a slave state was a terrible mistake. The Free Soilers rhetoric was taken up by the Republican party as it emerged in 1854.

The Republicans also argued that slavery was economically inefficient, compared to free labor, and was a deterrent to the long-term modernization of America. Worse, said the Republicans, the Slave Power, deeply entrenched in the "Solid South", was systematically seizing control of the White House, the Congress, and the Supreme Court. Senator and governor Salmon P. Chase of Ohio was an articulate enemy of the Slave Power, as was Senator Charles Sumner of Massachusetts.

In his celebrated "House Divided" speech of June 1858, Abraham Lincoln charged that Senator Stephen A. Douglas, President James Buchanan, his predecessor, Franklin Pierce, and Chief Justice Roger Taney were all part of a plot to nationalize slavery, as proven by the Supreme Court's Dred Scott decision of 1857.

Other Republicans pointed to the violence in Kansas, the brutal assault on Senator Sumner, attacks upon the abolitionist press, and efforts to take over Cuba (Ostend Manifesto) as evidence that the Slave Power was violent, aggressive, and expansive.

The only solution, Republicans insisted, was a new commitment to free labor, and a deliberate effort to stop any more territorial expansion of slavery. Northern Democrats answered that it was all an exaggeration and that the Republicans were paranoid. Their Southern colleagues spoke of secession, arguing that the John Brown raid of 1859 proved that the Republicans were ready to attack their region and destroy their way of life.

In congratulating President-elect Lincoln in 1860, Salmon P. Chase exclaimed, "The object of my wishes and labors for nineteen years is accomplished in the overthrow of the Slave Power", adding that the way was now clear "for the establishment of the policy of Freedom" — something that would come only after four destructive years of Civil War.