A military campaign in the American Civil War. By the autumn of 1862 the stronghold of the Confederacy forces at Vicksburg in western Mississippi was the last remaining obstacle to Union (Northern) control of the Mississippi River. In late 1862 advances by Generals Grant and Sherman failed to capture the city. In May 1863 Grant started a siege of the city. After six weeks of resistance, Vicksburg surrendered on 4 July. With its capture, the Confederacy was effectively split in half. The Union success at Vicksburg and Gettysburg in July 1863 marked a major turning-point in the Civil War.