Say, I hate to prophesy the future (1861) or be a stickler for future inconvenient facts, but in fact "the North" did allow "the South" to secede, peacefully, as Winfield Scott advised Lincoln on March 3, 1861, the North in effect said: "Wayward sisters, depart in peace".
What the North did not allow was the new peacefully formed Confederacy provoking war through dozens of seizures of Federal properties -- forts, ships, arsenals, mints, etc. -- starting war at Fort Sumter (April 12), formally declaring war on the United States (May 6, 1861) and waging war against the Union in Union states like Missouri and Maryland.
On February 18, 1861 Jefferson Davis promised there would be war if "the integrity of our territory and jurisdiction be assailed".
On March 4, Abraham Lincoln promised "In your hands, my dissatisfied fellow countrymen, and not in mine, is the momentous issue of civil war.
The government will not assail you.
You can have no conflict without being yourselves the aggressors."
On April 12 Davis decided the Confederacy's integrity was assailed at Fort Sumter, and so launched the assault which Lincoln took as an act of war:
Of course, all that is still years in the future, impossible to say today (February 1857) how such things might eventually play out. ;-)
There is a reason why the first thing Lincoln did was to throw up a commercial blockade. It had everything to do with money, and nothing to do with military advantage.
Interesting. Why did Davis decide the Confederacy’s integrity was assailed at Fort Sumter?