The North won control of almost all of the Mississippi River by capturing the cities along the river in the fall of 1862 and the spring of 1863. However, the Confederacy still held Vicksburg, an important city and fort. If they held, the Confederates could move soldiers and supplies from one side of the river to the other. Grant started the Siege of Vicksburg during the month of May 1863. The siege continued until July 4, 1863, when the Confederates there surrendered to Grant. That was one of the turning points in the war by dividing the Confederacy into two parts.