Long is best known for his opposition to the Civil War and being in favor of independence for the Confederacy on the basis of "states' rights". By 1864, Long's arguments on the institution of slavery had changed since his "free-soiler" days, and he argued against President Abraham Lincoln's Emancipation Proclamation because Long believed the proclamation only served to harden the resolve of Southerners as they continued to resist and prolong the war. In a speech he made in Congress on April 8, 1864, Long expressed his anti-war views, and he championed the "states' rights" arguments proffered by Vice President Thomas Jefferson and James Madison in their The Kentucky and Virginia Resolutions of 1798.