Abraham Lincoln, a self-taught lawyer, legislator and vocal opponent of slavery, was elected 16th president of the United States in November 1860, shortly before the outbreak of the Civil War. Lincoln proved to be a shrewd military strategist and a savvy leader: His Emancipation Proclamation paved the way for slavery’s abolition, while his Gettysburg Address stands as one of the most famous pieces of oratory in American history. In April 1865, with the Union on the brink of victory, Abraham Lincoln was assassinated by Confederate sympathizer John Wilkes Booth; his untimely death made him a martyr to the cause of liberty, and he is widely regarded as one of the greatest presidents in . history.
The Wilmot Proviso ultimately died in Congress and the debate over the slavery in the territories continued. The term, Slavery—United States—Extension to the Territories in the Subject Index produces a number of arguments against the Mexican War and the introduction of slavery into new territories, including “ Horace Mann's Letters on the Extension of Slavery into California and New Mexico .” Mann criticized the war with Mexico and claimed that it was merely a means for the South to add slave territories and states to the Union: