Abraham Lincoln spoke out against the expansion of slavery.
Abraham Lincoln . In doing so , he preserved the Union , paved the way to the abolition of slavery , strengthened the federal government , and modernized the economy . In 1858 , while taking part in a series of highly publicized debates with his opponent and rival , Democrat Stephen A. Douglas , Lincoln spoke out against the expansion of slavery , but lost the U.S. Senate race to Douglas . As the war progressed , his complex moves toward ending slavery included the Emancipation Proclamation of 1863 ; Lincoln used the U.S. Army to protect escaped slaves , encouraged the border states to outlaw slavery , and pushed through Congress the Thirteenth Amendment to the United States Constitution , which permanently outlawed slavery .