Answer: Dred Scott argued in the Scott v. Sanford case that, after traveling and staying with his master in a free state, he had been emancipated by that state's laws.
Explanation: Dred Scott increasingly exposed that many of the calls for popular sovereignty in establishing new territories as free or slave states relied heavily on the nullification by the courts of the laws of free states. Abraham Lincoln's campaign in 1860 relied heavily on noting how recent actions like the Kansas-Nebraska Act, Dred Scott, and the Fugitive Slave Act had refused to respect the North's laws concerning slavery and helped him win the election without southern support.