Lincoln, in his war address to Congress on July 4, 1861, made his views regarding secession clear and, I believe, is his longest treatment of the topic. It has always struck me as interesting that Lincoln thought it necessary to clearly distinguish between secession and rebellion, and took up so much time in an address to Congress to do so. Lincoln always understood that the war of ideas was just as important as the war on the battlefield, something some of our Presidents have failed to understand to their cost. A good summary by Mackubin Thomas Owens of how Lincoln’s position on secession had a long heritage among American statesmen prior to the Civil War may be read here. My own views on secession are set forth in the comments here. Lincoln on secession:
“It might seem at first thought to be of little difference whether the present movement at the South be called “secession” or “rebellion.” The movers, however, well understand the difference. At the beginning they knew they could never raise their treason to any respectable magnitude by any name which implies violation of law. They know their people possessed as much of moral sense, as much of devotion to law and order, and as much pride in and reverence for the history and Government of their common country as any other civilized and patriotic people. They knew they could make no advancement directly in the teeth of these strong and noble sentiments. Accordingly they commenced by an insidious debauching of the public mind. They invented an ingenious sophism, which, if conceded, was followed by perfectly logical steps through all the incidents to the complete destruction of the Union. The sophism itself is, that any State of the Union may, consistently with the national Constitution, and therefore lawfully and peacefully, withdraw from the Union without the consent of the Union or of any other State. The little disguise that the supposed right is to be exercised only for just cause, themselves to be the sole judge of its justice, is too thin to merit any notice.