I am currently rereading Gene Kizer Jr's book, Slavery Was Not the Cause of the War Between the States -- the Irrefutable Argument.
Kizer's book is very convincing in its argument that economics was the overriding factor for both South and North. If the South seceded, it rid itself of the huge tax burden foisted on it by the North. Its ports would attract shipping and imports, drawing substantial business and tax revenues away from the North. The North, on the other hand, would face economic devastation, so dependent was it on the South for its jobs, manufactures and tax revenues. In fact, immediately after the first seven states seceded, a depression began in the North and there was a growing financial panic.
These facts are not just Kizer's theories or interpretations. His conclusions are drawn from documents from the time period, including speeches, quotes from famous people, newspaper accounts, editorials, and the writings of economists. There is enough material there to give Northern apologists nightmares.
Another part of the book is a reprint of Charles Ramsdell's famous treatise on "Lincoln and Fort Sumter." This essay describes in detail, minute by minute in some cases, the Fort Sumter controversy, who did what and when.
The crux of the Fort Sumter problem was this: South Carolina had seceded from the Union, and wanted control over the fort that was located within its own borders. Lincoln was faced with a dilemma: if he gave up the fort, he admitted to the legality of secession, and opened Charleston Harbor to tariff-free imports from Europe. He had to start the war, but knew he must not be seen as the aggressor. What to do? Ramsdell does not draw any conclusions for you, but the facts point irrefutably to Lincoln's plan to start the Civil War by forcing the South to fire the first shot.
Lincoln was a tyrant, but a crafty one.