The decision for war had been made by Davis on April 10th when is sent orders to Beauregard to demand the immediate surrender of Sumter and, if refused, to shell it into submission. The Harriet Lane could have done nothing and the confederate shelling of Sumter would still have started on the 12th. Prior to the 11th, Sumter had not interfered with shipping into and out of Charleston. The garrison there had committed no hostile acts. Still the order went out to demand surrender or face shelling. So your suggestion that the south was forced into it by Northern obstruction of trade is wrong.
The order that Davis gave to fire on Sumter started the war, just as Davis had known it would do. For his own reasons he preferred war to negotiation.
The decision for war had been made by Davis on April 10th when is sent orders to Beauregard to demand the immediate surrender of Sumter and, if refused, to shell it into submission. One could just as easily say that the decision for war had been made by Lincoln in December 1860 or February 1861 when he directed Winfield Scott and other military officials to make preparations for retaking the southern forts. That does not change the fact though of who fired the shot initiating the physical hostilities, that being the Harriet Lane.