From the Compromise of 1850, the South gained the reinforcement of the fugitive slave laws with the passing of the Fugitive Slave Act of 1850. This law required that all escaped slaves that were captured must be returned to their masters, and both citizens and officials of the free States had to cooperate too.
Abolitionists also called this Fugitive Slave Act the "Bloodhound Law" because of the dogs used to track down and chase slaves.