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The northern government led by A. Lincoln understood very well that they could maneuver the south into firing on them - thus winning a point in the war of public opinion. So they did that very thing. So the north proceeded to make the south look bad. The first shots of the war were fired before that, however, by union soldiers at an arsenal in Florida. They fired on unarmed civilians. Easy enough to find if you look for it. I believe the Florida National Guard web site mentions this, for example. The south could not back down and proved it was determined to defend itself. Up till then (see, for example, Thomas J. DiLorenzo's books: The Real Lincoln and Lincoln Unmasked for much detail) - up till then, it was well understood that the union would never be preserved by one state aggressing on another. It was understood that the central government was created by sovereign states who could uncreate it, and which were superior to it. It was understood that all states had the full and complete right to withdraw from the uniting of states. The very foundation of the country was itself a secession from England, for goodness' sake!