In war and love, the last victory tends to be decisive, Dave.
But I'm not belittling his military genius. The South did well initially and Lee was a skilled General. The North was a sleeping giant though, and - as Rhett Butler had prophesied to Scarlett's chagrin at that fateful party at Tara at the beginning of the Civil War - it was only a matter of time until it would win given its stronger industry and larger manpower. The war would have needed to be finished within 12-18 months for the South to win it, from then on it was a case of diminishing returns for the South.
When Hitler declared war on the US after Pearl Harbor, a look into the history books on the Civil War could have taught him a thing or two. Or he should have spoken to Clark Gable first.