This would be the siege of Vicksburg. This battle was an important part of the war for the north because it started out a train of victories.
The fall of Vicksburg, Mississippi on July 4, 1863 gave the Union full control of the river from its source to its mouth.
The fall of Vicksburg, Mississippi on July 4, 1863, gave the Union control of the river along its entire length.
Vicksburg
Control of the Mississippi was the big objective. Soon after the fall of Vicksburg in July 1863, the Union controlled the whole river, denying the Confederates all use of this big military highway, and isolating all enemy units to the West of the river.
By the Union capturing Vicksburg and Port Hudson they took complete control over Mississippi river.
Mississippi River
The fall of Vicksburg on the Mississippi, last major Confederate river-port. This isolated all Confederate units to the West of the river.
Vicksburg was the last major Confederate stronghold on the Mississippi River because of its strategic location, which allowed control over river traffic and supply routes. Its high bluffs provided a defensive advantage, making it difficult for Union forces to capture. The fall of Vicksburg in July 1863 effectively split the Confederacy, giving the Union complete control of the Mississippi River and a critical victory in the Civil War.
It deprived them of the use of this important highway for the transport of men and materials. When the whole river was liberated (after Vicksburg), all Confederate units to the west of it were isolated.
With the fall of Vicksburg on July 4, 1863, the Federals gained full control of the Mississippi River and thus cut the Western Confederacy (Trans Mississippi District) off from the eastern two thirds of the Confederacy. Control of the Mississippi was vital to the Union's Anaconda Plan which was intended to strangle the Confederate supply lines both foreign and domestic.
In 1863, the Union forces captured Vicksburg, Mississippi, which was a critical stronghold for the Confederacy along the Mississippi River. This victory, along with the capture of Port Hudson shortly after, effectively divided the Confederacy in two, disrupting their supply lines and communication. The fall of Vicksburg marked a significant turning point in the Civil War, enhancing Union control over the Mississippi River.
Capturing the Confederate city of Vicksburg was worth the numbered separate Union campaigns to do so. This was because of its strategic position on the Mississippi River. The Union wanted to control the entire river in order to secure a good position on the western front. But not only that, as Vicksburg was a center for receiving supplies to the west of the city and shipping them to various parts of the South. As it came to be, Vicksburg could only be taken via a long siege. The city basically reached a point of starvation. It gave the Union army control of the Mississippi River