The Fugitive Slave Act was a law passed by the United States Congress on 18 September 1850 as a part of the Compromise of 1850. The act stated that any captured slaves had to be returned to their masters, even if they had been caught in free states; the act was passed in an attempt to combat the abolitionist Underground Railroad. President Millard Fillmore signed the law in hopes of making peace between the north and south to prevent a war.