The right of revolution is an inherent one. When people are oppressed by their government, it is a natural right they enjoy to relieve themselves of oppression, if they are strong enough, whether by withdrawal from it, or by overthrowing it and substituting a government more acceptable.
The issue of slavery provoked little moral indignation in General Grant, and in the first days following the attack on Fort Sumter, he seems to have believed that the North shared his indifference to abolition: "In all this I can but see the doom of Slavery. The North do not want, nor will they want, to interfere with the institution. But they will refuse for all time to give it protection unless the South shall return soon to their allegiance, and then too this disturbance will give such an impetus to the production of their staple, cotton, in other parts of the world that they can never recover the controll of the market again for that comodity. This will reduce the value of negroes so much that they will never be worth fighting over again."
In his later reminiscences, Ulysses S. Grant roundly condemned the Mexican War in which he had served, and even saw the Civil War as a sort of karmic retribution for America's sins against its southern neighbor: "Generally the officers of the army were indifferent whether the annexation [of Texas] was consummated or not; but not so all of them. For myself, I was bitterly opposed to the measure, and to this day regard the war, which resulted, as one of the most unjust ever waged by a stronger against a weaker nation. It was an instance of a republic following the bad example of European monarchies, in not considering justice in their desire to acquire additional territory."