Regardless of why South Carolina said it was seceding in its "declaration of independence," Lincoln initially fought the war to keep the union whole. From everything I've read over the years, he would have been willing to codify slavery into law further to save the union. The civil war was not fought to free the slaves, as Draco wrote. Quite the opposite, it was fought (by the South) to assure slavery remained in force.
Very good! I have read about Lincoln extensively (reading Team of Rivals now) and Sandburg was OK but not my favorite.
I think the war was fought over the railroads. You see, there was a divide in congress between slave states and non slave states. The divide became greater and much heavier in the non slave states' favor due to the missouri compromise, which stated that no new state entering the union could be a slave state. Meanwhile, the government was granting land in the North to build a complete railway system. If you look at a map of the railroads from back then, you'll see the railroads in the south had short lines that went from Atlanta to Charleston. You'll see the railroads in the north run coast to coast, and Chicago (famous for its stockyards) the hub of much of it. Consider the economic benefit of being able to get your goods to market in the North vs. having to use wagon train to get your cotton or tobacco to the Mississippi river or to the coast.
River and Canal traffic move the goods in the South to the Atlantic or Gulf ports. However, the Railroad was the hallmark of the industrial North and industrial barons. Tariffs protected all of their production and more, even the products not produced in the north. The Southern States paid these tariffs on their imports which provide revenue to the Federal government which spent the money largely in the industrializing North. This Tariff protected industrialization was of the Hamilton economic philosophy, the Whig party as the name changed to Republican. It also supported dominance of the Federal government over State rule as the Constitution defines. The South was predominately followers of the Jeffersonian Republic State rule government as opposed to the Hamiltonian Federal system. Lincoln was the first Republican President since the party changed the name from Hamilton's Whig party. Basically the Industrializing North was exploiting the Agrarian South and the election of Lincoln, a hard core Hamiltonian Tariff supporting Whig tipped the cart over. The Republicans of that day are not the same party as today, both parties have nearly reversed there philosophy since the days of Lincoln. The Republicans held sway for many years until Wilson managed to make the Democrats look more like Hamiltonians, Then the Republicans began to counter by becoming more like Jeffersonian Democrat/Republicans. Franklin Roosevelt/Truman-Kennedy/Johnson long run forced the morphing of the Republicans farther toward the Jeffersonian philosophy with the complete reversal of the South from Democrat to Republican. During Wison's time the Hamiltonians Preferred the Label "Progressive" until it gathered a bit of ill will, but the term has made a resurgence again. I view Lincoln as the first Progress, Teddy Roosevelt the next (even though Republican). Actually the War is not over, but Lincoln was the only President to take the battle to armed conflict up to this point and I am not at all sure how this act will close.
