The one who starts the war is not the one who fires the first shot, but the one who causes the first shot to be fired. 

In order to coalesce the forces in the North, Lincoln had to stage an incident to inflame the populace, which he did. The firing on Sumter was by his own admission a setup for just such action. Lincoln was aware that provisioning Sumter could provoke a war.

The Providence Daily Post said “For three weeks the administration newspapers have been assuring us that Ft. Sumter would be abandoned”, but “Mr. Lincoln saw an opportunity to inaugurate civil war without appearing in the character of an aggressor”. 

The Jersey City American Standard wrote concerning Lincoln’s behavior, “there is a madness and ruthlessness which is astounding… this unarmed vessel… is a mere decoy to draw the first fire from the people of the South, which act, by the predetermination of the government, is to be the pretext for letting loose the horrors of war.”