How The South Could Have Won The War.
How Could The South Have Won?
How could the South have won the Civil War? The best possibility of Confederate victory would have been from intervention by Britain (and possibly other European powers), just like the alliance with France that the United States formed that led to victory in the American Revolution. Despite some fluctuating moments, however, Britain withheld its support, partly because British leaders had been against slavery for a very long time, and they found it hard to gain public support of a slave-holding country. Another factor was the fact that at the same time Britain was engaged in a expansive adversarial dialogue with Russia. The Russians were worried that a Confederate victory, and the subsequent permanent split of the United States would leave no power to counter Britain to the west. Russia made it clear that it would crank up the rhetoric, and possibly its military if Britain were to help the South. 
The only other realistic possibility  of a Confederate victory would have come from the "power of contingency.", as James McPherson calls it. He argues that the outcome of the war, Britain's staying out, and also Abraham Lincoln's re-election in 1864 were all adherent, upon the interrelation of other events.
McPherson also points out that the turtle-slow progress of the Union army during the summer of 1864 presented an obstacle to the Union's victory: "If the election had been held in August 1864 instead of November, Lincoln would have lost. He would have gone down in history as an also-ran, a loser unequal to the challenge of the greatest crisis in the American experience."  McPherson's formularization suggests that if the Confederacy had slowed the Union's progress for three months or more, they could have won.