The turning point of the Civil War is usually considered Gettysburg but before then, the south was winning the war. After Grant and Sherman, the war was tilted to the North but under McClellan the North didn't win many battles because of his reluctance to push forward and fight the offensive.
I disagree entirely. While the Confederacy won an early initial victory at Manassas/Bull Run, the overall picture for the South for much of late 1861 and 1862 (the period in which the South stood on the strategic defensive) was incredibly gloomy. Let's run through the list of disasters briefly. November 7 1861: the US Navy seizes Port Royal, South Carolina, thus driving a wedge between Charleston and Savannah. January 19, 1862: the Confederate army in eastern Kentucky is routed at Mill Springs, opening the way for a Union invasion of Tennessee. February 6: Fort Henry falls to US Grant, opening the Tennessee River to the Union. February 16: Fort Donelson is surrendered, opening the Cumberland to Union troops and gunboats. April 6: the combined western Confederate army fails to break Grant's army at Shiloh, and with the arrival of Don Carlos Buell's forces, are forced to withdraw, making the fall of Corinth inevitable. Finally, McClellan, despite his flaws, comes within a few miles of Richmond before being driven away by an inferior, but very aggressively commanded Confederate Army of Northern Virginia.
It is true that a period of Confederate superiority followed in the east. But even for the year or so that the Army of Northern Virginia was dominant, the Confederacy continued to collapse steadily in the west.
By Southern Defensive War, are you referring to the battles for control of the Mississippi river?