Northern success in the Siege of Vicksburg was important because
the Union had a plan called the anaconda plan. The
anaconda plan is when the Union planned to cut the Confederacy in
half. By doing this, the Confederacy would not have any way to
obtain (get) supplies (food, clothes, weaponry, etc.) When
the siege of Vicksburg was a success, the Union was able to carry
out the anaconda plan since the Mississippi River is in Vicksburg,
and by taking over the Mississippi River, that split the
Confederacy into two.