Final answer:
Grant's victory at Vicksburg, combined with Admiral Farragut's capture of New Orleans, gave the North control of the Mississippi River.
Step-by-step explanation:
The North gained control of the Mississippi River through Grant's victory at Vicksburg and Admiral David Farragut's capture of New Orleans. In the spring and summer of 1862, the Union navy under Admiral Farragut fought past the forts guarding New Orleans and fired upon the city. Confederate forces, led by General Lovell, sent their artillery upriver to Vicksburg after realizing they could not defend New Orleans.
This allowed the Union to gain control of New Orleans and Memphis, and eventually led to Grant's capture of Vicksburg, giving the North control over the Mississippi River.