The Fugitive Slave Law was enacted in the United States in 1850 as a result of the passage of a related act by the U.S. Congress. As part of the Compromise of 1850 between the Northern antislavery and Southern pro-slavery contingents in the United States, the new law referred to an existing law from 1793 that gave slave owners the right to enter another state and recapture runaway slaves who had previously belonged to them. According to the law, it was the responsibility of the federal government to help owners recapture these slaves, who were denied any legal means to try and fight their return to slavery. After the Fugitive Slave Law led to many conflicts between Northern abolitionists and Southern slave owners in the 1850s, the outbreak of the U.S. Civil War at the start of the next decade essentially rendered the law meaningless.
Until 1850, the laws concerning fugitive slaves who had fled to the North were exceedingly vague. A 1793 law ensured that slave owners could cross state lines and take their slaves back, all while denying captured slaves basic rights like habeas corpus, jury trial, or the right to testify on their behalf. Northern states reacted by enacting personal liberty laws that guaranteed these rights to the former slaves. An 1842, U.S. Supreme Court ruling on a fugitive slave case declared that a slave owner's rights outweighed these personal liberty laws, but it also stipulated that a state need not cooperate in any way with the recapture of fugitive slaves, deeming it a federal responsibility.
One of the stipulations that Southern politicians insisted was necessary to be included in the Compromise of 1850 was a stronger Fugitive Slave Law. The one that Congress passed that year put U.S. marshals in charge of aiding slave owners with the recapture of runaway slaves. It also placed the burden of proof upon slaves to prove they weren't runaways, even as it denied them the basic legal rights to effectively do so. All that was necessary for a slave owner to prove that the man in question was his former slave was an affidavit from a Southern state court or the testimony of white witnesses.
Many Northern states continued to harbor fugitive slaves and went to great lengths to circumvent the Fugitive Slave Law. The famed Underground Railroad of antislavery sympathizers helped deliver many of these former slaves to friendly Northern states or even Canada. There were even armed conflicts between those protecting the slaves and the owners and federal personnel demanding their return. Bitterness over the law increased the animosity between the North and South leading up to the Civil War.
When the U.S. Civil War began in 1861, the states in the North who claimed to be beholden to a higher law simply ignored the Fugitive Slave Law. They legally justified this response by claiming that since they were at war with the South, the fugitive slaves were part of the contraband of that war and need not be returned. All slaves gained their freedom at the conclusion of the war following passage of the 13th Amendment to the U.S. Constitution.
