Alex Bargmann, Studied U.S. History in Undergrad
The United States Congress passed the Fugitive Slave Act in 1850, even though the Supreme Court had decided, in 1842, that a state was not obligated to return or prosecute an escaped slave. Vermont threatened to nullify the law, during this period nullification was an important federal issue - a driving one behind the Civil War. President Fillmore threatened to use federal forces to enforce the law in Vermont.
With the outbreak of the Civil War, the law was not followed - officially repealed in 1864.
We have two longer videos on the Act that may be useful: