MAP 13.2 Battles of Gettysburg and Vicksburg, 1863 The three-day battle in Gettysburg and the six-week siege of Vicksburg led to critical victories for the Union. Together, these victories forced General Lee’s troops back into Confederate territory and gave the Union control of the Mississippi River. Still, the war was far from over. Confederate troops controlled the southern heartland, and Northerners wearied of the ever-increasing casualties.