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The personal liberty laws were a series of laws passed by several U.S. states in the North in response to the Fugitive Slave Acts of 1793 and 1850.
The laws were designed to protect free blacks, freedmen, and fugitive slaves by effectively nullifying the Fugitive Slave Law without actually invoking the controversial doctrine of nullification. This was done through provisions such as forbidding the use of state jails to imprison alleged fugitives, to prevent state officials from enforcing the strict law, and compelling slave bounty hunters to furnish corroborative proof that his captive was a fugitive, as well as according the accused the rights to trial by jury and appeal. Laws in some states made it easier to extradite a runaway if slave status were confirmed.
In Prigg v. Pennsylvania (1842), the U.S. Supreme Court determined that personal liberty laws were unconstitutional. The court held that the laws interfered with the Fugitive Slave Act and that while states were not compelled to enforce the federal law, they could not override it with other enactments.
The Prigg decision caused several Northern states to amend their laws, which specified that law enforcement officials and jurists refrain from doing anything about runaway slaves. The only other option left to slave catchers was to kidnap runaways, and then either return them to their owners, or force them to appear before federal judges who were not held to state statutes.
During the American Civil War, some of the Northern states agreed to repeal these bills if it meant that all Confederate states would rejoin the Union. The Rhode Island state legislature repealed their law in January 1861 in hopes of preserving the Union.