A misunderstanding on my part then. When you said that for two years the South had the best of the war I thought you were saying that they were winning.
Possibly "winning," like "beauty" was in the eyes of beholders?
Clearly in 1861 the South believed they could win a war, otherwise they would have used a different strategy -- perhaps more conciliatory and, dare I say it, Constitutional?
If they had believed they were going to lose a war, they may have attempted, for example, applying to Congress to secede.
But also clearly, they had no such thoughts -- they expected to win, and that's why they did everything to provoke a war, of which Fort Sumter was just the final straw.
And throughout 1861, the Confederacy was on the march -- expanding from seven states to eleven after Sumter, sending their forces into Union states of Maryland, Kentucky, Missouri, the pro-Union counties of Western Virginia, North Carolina and Eastern Tennessee, as well as western territories like Oklahoma and New Mexico.
The South also achieved a number of military victories, the most important being at Manassas / Bull Run, but also Wilson's Creek and Lexington in Missouri (a Union state), Balls Bluff in Barber, VA, and just to mention the famous exploits of the Confederate cavalry officer, Nathan Bedford Forest at Caseyville, Eddysville (Nov 24) and Sacramento (Dec 28) in Kentucky (a Union state).
So, at the end of December 1861, on the first anniversary of South Carolina's secession, your average southerner could look around and note with some satisfaction the military and political accomplishments of his Confederacy.
Indeed the first major Union victories did not begin until January (Mills Springs, KY) and February (Fort Henry, Tennessee, then Burnside at Roanoke, North Carolina) of 1862.
But when, exactly, did your average southerner begin to realize his cause was lost?
Certainly not in 1862, I'd say, possibly after Gettysburg and Vicksburg in 1863, but just as likely, not until Sherman took Atlanta in 1864.
And the point of all this was to answer jessduntno's claim that Lincoln's Emancipation Proclamation was the cause of the change in the North's military fortunes.
It wasn't. There was a change -- or at least a perceived change -- at Antietam, but that's what allowed Lincoln's Proclamation, the Proclamation did not cause it.