Why were the siege of Vicksburg and the battle of Gettysburg crucial to the outcome of the war?

The two
Union victories, which occurred almost simultaneously (Gettysburg on July 3 and Vicksburg on
July 4, 1863) were together arguably the turning point of the war, though some might dispute
this because the war dragged on for another year and nine months, with some of the heaviest
fighting and worst casualties during that period. Of the two engagements in question, many
Americans would be surprised at the claim that Vicksburg was the more important. Grant's victory
there meant that the Mississippi River was now under Union control. The Confederates were no
longer able to use it for transportation and the supplying of their armies, and the Confederacy
was now effectively split in two. There was also a psychological component to the Union victory
that is often overlooked. The advantage the South had from the start was the vastness of its
territory and the fact that Confederate forces merely had to fight a defensive war in order to
win. The burden of conquest lay entirely upon the...