The Fugitive Slave Act was passed by the United States Congress on September 18, 1850, as part of the Compromise of 1850 between Southern slave-holding interests and Northern Free-Soilers. The Act required all escaped slaves, upon capture, be returned to their owners and that officials and citizens of free states had to cooperate in this law enforcement. It was one of the most controversial elements of the compromise and heightened tensions that ultimately led to the Civil War.