Final answer:
The siege of Vicksburg in May 1863, led by Major General Ulysses S. Grant, resulted in the Union's control over the Mississippi River and divided the Confederacy. This strategic victory was a turning point in the Civil War, as it compromised Confederate transportation and split their territory.
Step-by-step explanation:
The siege in question, which gave Union forces complete control of the Mississippi River and split the South in two, was the siege of Vicksburg. Led by Major General Ulysses S. Grant, Union forces laid siege to Vicksburg in May 1863 after several unsuccessful attempts to take the Confederate stronghold. Victory at Vicksburg was crucial because the city was strategically located on a bluff overlooking the Mississippi River, a point from which river traffic could be controlled. A successful siege here meant cutting off the Confederacy's most significant water route and dividing their territory. Grant's persistent efforts, which included cooperation with the Union Navy and previous battles like Shiloh, culminated in a well-conducted siege that eventually forced the Confederate forces, outnumbered 77,000 to 33,000, to surrender. On July 3, 1863, after more than a month of enduring the siege, the Confederates finally surrendered, handing a significant victory to the Union and inflicting a serious blow to the Confederate war effort.