Lincoln, the leader most associated with the end of slavery in the United States, came to national prominence in the 1850s, following the advent of the Republican Party, whose official position was that freedom was "natural," the natural condition of all areas under the direct sovereignty of the Constitution, whereas slavery was "exceptional" and sectional. Earlier, as a member of the Whig Party in the Illinois General Assembly, Lincoln issued a written protest of the Assembly's passage of a resolution stating that slavery should not be abolished in the District of Columbia. In 1841, he won a court case ("Bailey v. Cromwell"), representing a black woman, Nance Legins-Costley, and her children who claimed she had already been freed and could not be sold as a slave.