He did believe that he had the right to use violence to prevent States from leaving the Union.
Preserving the Union was his causus belli.
People ought to read his own words."
Yes, you should certainly read Lincoln's First Inaugural words, since they are key to understanding what happen next.
Lincoln promised Confederates that he would not interfere with them beyond what was required by Federal law (i.e., mail, tariffs), and they could not have war unless they themselves started it.
Those were Lincoln's peace terms in March, 1861: don't start a war, and you can't have a war.
But the Confederacy took Lincoln's terms as a declaration of war, and ordered up troops and preparations for military assault on Fort Sumter, a unequivocal act of war against the United States Army.
So, six months after December 1860, when the Confederacy first provoked, later started and then formally declared war on the United States, raising up a 500,000 man army, sending military aid to pro-Confederates in Union Missouri, then, finally Lincoln directly confronted that existential threat.
Remember: by June 10, 1861, when that first Confederate soldier (Pvt. Henry Wyatt of North Carolina), was killed at the Battle of Big Bethel, dozens of Union troops had already died, over 100 wounded and 500 captured and held as POWs.
So the Confederacy was waging war against the United States for months before Lincoln seriously confronted it.
Of course, once Lincoln began to respond to Confederates' war, he devised a long-range plan to utterly defeat and destroy the rebellion.
Perhaps the most foresighted politician of the time was Lincoln's rival and Secretary of State, William Seward, who came to hugely admire Lincoln, writing in June 1861:
- "Executive skill and vigor are rare qualities.
The President is the best of us, but he needs constant and assiduous cooperation."
Had Seward himself been elected President, the outcome of secession and Confederacy would certainly have been different, but Seward came to admire and fully supported Lincoln's leadership.
