At its peak, nearly 1,000 slaves per year escaped from slave-holding states using the Underground Railroad – more than 5,000 court cases for escaped slaves were recorded – many fewer than the natural increase of the enslaved population. The resulting economic impact was minuscule, but the psychological influence on slave holders was immense. Under the original Fugitive Slave Act of 1793, officials from free states were required to assist slaveholders or their agents who recaptured runaway slaves. But, citizens and governments of many free states ignored the law, and the Underground Railroad thrived.
With heavy lobbying by southern politicians, the Compromise of 1850 was passed by Congress after the Mexican–American War. It stipulated a more stringent Fugitive Slave Law; ostensibly, the compromise addressed regional problems by compelling officials of free states to assist slave catchers, granting them immunity to operate in free states. Because the law required sparse documentation to claim a person was a fugitive, slave catchers also kidnapped free blacks, especially children, and sold them into slavery. Southern politicians often exaggerated the number of escaped slaves and often blamed these escapes on Northerners interfering with Southern property rights. The law deprived suspected slaves of the right to defend themselves in court, making it difficult to prove free status. In a de facto bribe, judges were paid a higher fee ($10) for a decision that confirmed a suspect as a slave than for one ruling that the suspect was free ($5). Many Northerners who might have ignored slave issues in the South were confronted by local challenges that bound them to support slavery. This was a primary grievance cited by the Union during the American Civil War, and the perception that Northern States ignored the fugitive slave law was a major justification for secession.