The significance of General Ulysses S. Grant's victory at the siege of Vicksburg is best represented by option:
D) It helped the Union establish control of the Mississippi River.
The victory at Vicksburg in July 1863 was crucial because it gave the Union full control of the Mississippi River, effectively splitting the Confederacy in two and disrupting their supply lines. This strategic gain was a turning point in the Civil War, enhancing the Union's ability to move troops and supplies while challenging Confederate movement and logistics.