The Confederate Army was not as good as the Union Army during the Civil War. There is a simple and logical reason the Confedrates won several battles during the early stages of the war. After John Brown's raid on Harper's Ferry in 1858, Southerns became convinced a full scale northern attack was imminent. They already had existing state militia units to put down potential slave revolts and believing they faced imminent attack these militia units grew into regular army units preparing for war. While the South was preparing for war the peacetime army in the north was virtually nonexistent.
You can't be serious? It was half the size of its Union adversary on which it inflicted far greater casualties and took four years to subdue? Not as good, really?
That they won "several battles during the early stages" is an understatement. And they had no head start in preparing for war - the armies were raised at seccession. There were state militias in evey northern state, in addition to the standing U.S. Army, albeit small at the time.
If there was a "simple and logical reason" for that Army's performance on the battlefield, the whole thing would have been long forgetten. It's too bad General Schwarzkopf died a couple years ago and can't stop in to DCUM and explain.