Grant's capture of Vicksburg did that.
By capturing Vicksburg and liberating the Mississippi. This gave them control of this important military highway, and isolated all enemy units ot the West of the river.
As a sign that they did not recognise the Confederacy.
Grant was able to gain control of the Mississippi for the Union, denying its us to the Confederacy. It prevented the Mississippi Valley states from receiving supplies and reinforcements from Texas and Arkansas, and it allowed Union forces to concentrate on the Deep South without fear of attack from the rear.
Vicksburg
The Siege of Vicksburg (May-July 1863) split the Confederacy by giving control of the Mississippi River to the Union forces. The city and as many as 30,000 soldiers surrendered on July 4, 1863.
During the American Civil War, two battles in particular helped the Union gain control of the Mississippi River. The first took place in 1862 and culminated in the capture of New Orleans by Union forces. The second took place in 1863 and ended with the Union capture of Vicksburg (Mississippi).
Vicksburg. It split the Confederacy in two, isolated the forces to the West of the river, and denied the enemy the use of this important waterway for the movement of men and materials. By ending the war in the Western theatre, it released Grant for important work in Tennessee.===================================================Falling to the Union forces after a 40 day siege, the Confederate defeat at Vicksburg is considered a major turning point in the Western theater of the Civil War. When the Confederate garrison surrendered their fortifications on July 4th, 1863, the Union military gained complete control of the Mississippi River.
Vicksburg's location was strategic because it sat on a 200-foot bluff above the Mississippi River. Capturing Vicksburg would sever the Trans-Mississippi Confederacy from that east of the Mississippi River and open the river to Northern traffic along its entire length.
Blockade the Southern ports, to starve the Confederacy of supplies. Liberate the Mississippi. Then send in armies of invasion to attack the South's weakened and starving forces.
The Union or Federal forces opposed the Confederacy.
During the American Civil War, controlling the Mississippi River was an important part of the overall Union strategy for two reasons. It would, first of all, cut the South in two and thereby weaken it militarily and otherwise. Second, it would open up the Deep South to invasion by Union land forces.
Mississippi Armed Forces Museum was created in 1984.