What compromise required all states to return slaves to their owners?

The compromise that required all states to return escaped slaves to their owners was the Fugitive Slave Act of 1850. This law was part of the Compromise of 1850, which aimed to ease tensions between free and slave states. It mandated that escaped slaves found in free states be returned to their enslavers, and imposed penalties on those who aided runaway slaves. This act intensified the national debate over slavery and contributed to the rising tensions leading up to the Civil War.