In his one-volume book on the Civil War James McPherson considers the explanations of other historians for why the U.S.A. won and the C.S.A. lost. He dismisses them all, including the enormously greater resources of the U.S., as suffering from the “fallacy of reversibility,” (I have looked up fallacy of reversibility previously and could find no cite to any other work than McPherson’s) that is, if conditions had been reversed the outcome would have been different. Which, yeah, if the South had the population base, the railroad infrastructure, if it had come into the mid-19th century and industrialized as the U.S. did instead of remaining an Egyptian slave economy from B.C., yeah things would likely have been different. I don’t know how that is a fallacy so much as an obvious fact. Rather, McPherson puts the reasons for the outcome on "the element of contingency." There were three or four points in the war, he argues, where if things had gone differently, the outcome would have been different. (How that is not reversibility, fallacious or not, I do not know.)

I reject McPherson's contingency explanation. The United States was going to win this war because of its superior resources as soon as 1) Abraham Lincoln committed the federal government to winning it at all costs, which he did very early on, and 2) Lincoln found fighting generals. Lincoln remarked after one U.S. debacle, it may have been Fredericksburg, that if the proportional losses in that battle (and the U.S. lost men at a better than 2-1 rate) held in every battle the Confederates would soon be out of manpower to continue the fight. It was inevitable, historians resist inevitability tooth and nail, and it was prolonged for four years because the Confederate States of America were fighting a defensive war on their own territory, and because of superior generalship. 

If Lee had accepted Scott's offer to lead the Army of the Potomac the war would have been over sooner; if Lee hadn't gotten out over his skis and invaded Pennsylvania the war would have lasted longer (but those commit the fallacy of reversibility). It would have taken longer or shorter but the outcome was going to be the same.