Final answer:
The capture of Vicksburg, Mississippi, led by Union General Ulysses S. Grant, was a significant victory that gave the Union control of the Mississippi River around the same time as the Battle of Gettysburg.
Step-by-step explanation:
The major victory in the South that gave the Union strategic control of the Mississippi River at about the same time as the Battle of Gettysburg was the capture of Vicksburg, Mississippi. This significant event took place under the leadership of Union General Ulysses S. Grant. The fall of Vicksburg to Union forces not only resulted in Union victory but was also pivotal in cutting the Confederacy in two and maintaining complete control over the Mississippi River, which was a strategic objective for the North during the Civil War.