Lincoln's bedrock position in 1860 was that slavery not be allowed to expand into the national territories. He knew that if slavery were restricted to the area it currently occupied, it would die. The slavers knew it to.
But, without preservation of the Union, slavery would -not- die.
Lincoln had a very powerful intellect; he also had common sense.
Walt
"Though he loved Caesar less than Rome, though the Union was more to him than our freedom or our future, under his wise and beneficent rule we saw ourselves gradually lifted from the depths of slavery to the heights of liberty and manhood; under his wise and beneficent rule, and by measures approved and vigorously pressed by him, we saw that the handwriting of ages, in the form of prejudice and proscription, was rapidly fading away from the face of our whole country; under his rule, and in due time, about as soon after all as the country could tolerate the strange spectacle, we saw our brave sons and brothers laying off the rags of bondage, and being clothed all over in the blue uniforms of the soldiers of the United States; under his rule we saw two hundred thousand of our dark and dusky people responding to the call of Abraham Lincoln, and with muskets on their shoulders, and eagles on their buttons, timing their high footsteps to liberty and union under the national flag; under his rule we saw the independence of the black republic of Haiti, the special object of slave-holding aversion and horror, fully recognized, and her minister, a colored gentleman, duly received here in the city of Washington; under his rule we saw the internal slave-trade, which so long disgraced the nation, abolished, and slavery abolished in the District of Columbia; under his rule we saw for the first time the law enforced against the foreign slave trade, and the first slave-trader hanged like any other pirate or murderer; under his rule, assisted by the greatest captain of our age, and his inspiration, we saw the Confederate States, based upon the idea that our race must be slaves, and slaves forever, battered to pieces and scattered to the four winds; under his rule, and in the fullness of time, we saw Abraham Lincoln, after giving the slave-holders three months' grace in which to save their hateful slave system, penning the immortal paper, which, though special in its language, was general in its principles and effect, making slavery forever impossible in the United States. Though we waited long, we saw all this and more."
-- Frederick Douglass, 1876
Walt