The South had a very brief opportunity early in the War, if they continued to push into the North. The North was not ready for an invasion and the South was not prepared to invade. The timing was very short because as soon as the North recognized they had a real war, the South effectively lost. The South could not win a war of attrition and lacked the industry to provide for a long term war. The only question was how long until they recognized that and how long it took for Lincoln to find U.S. Grant.
So, I am basically saying it was a war the South could not win. Instead, we had to experience 750,000 casualties before it ended.
Had the south attacked from Monocacy in 1861 instead of Bull Run, could the South actually changed the war’s trajectory? I don’t think the Battle of Fort Stevens is the same failure in 1861 as it was in 1864.