Some Northern states passed "personal liberty laws", mandating a jury trial before alleged fugitive slaves could be moved. Otherwise, they feared free blacks could be kidnapped into slavery. Other states forbade the use of local jails or the assistance of state officials in the arrest or return of such fugitives. In some cases, juries simply refused to convict individuals who had been indicted under the Federal law. Moreover, locals in some areas actively fought attempts to seize fugitives and return them to the South.
The Missouri Supreme Court routinely held that voluntary transportation of slaves into free states, with the intent of residing there permanently or definitely, automatically made them free. The Fugitive Slave Law dealt with slaves who went into free states without their master's consent. The U.S. Supreme Court ruled, in Prigg v. Pennsylvania (1842), that states did not have to offer aid in the hunting or recapture of slaves, greatly weakening the law of 1793.
The Fugitive Slave Act brought a defiant response from abolitionists. Reverend Luther Lee, pastor of the Wesleyan Methodist Church of Syracuse, New York wrote in 1855:
I never would obey it. I had assisted thirty slaves to escape to Canada during the last month. If the authorities wanted anything of me, my residence was at 39 Onondaga Street. I would admit that and they could take me and lock me up in the Penitentiary on the hill; but if they did such a foolish thing as that I had friends enough on Onondaga County to level it to the ground before the next morning. The slaves could no longer take control over what they could never imagine.
In 1854, the Wisconsin Supreme Court declared the Fugitive Slave Act unconstitutional in a case involving Joshua Glover, and Sherman Booth.
Other opponents, such as African American leader Harriet Tubman, simply treated the law as just another complication in their activities. The most important reaction was making the neighboring country of Canada the main destination of choice for runaway slaves.
With the outbreak of the American Civil War, General Benjamin Butler justified refusing to return runaway slaves in accordance to this law because the Union and the Confederacy were at war: the slaves could be confiscated and set free as contraband of war. The North also argued that the Fugitive Slave Act only applied to the Union; the South had broken away, so the law did not apply to the Confederacy.
Incidents involving fugitive slaves:
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