From the time the Civil War started in April 1861, both the North and South made controlling the Mississippi River a major part of their strategy. The Confederacy wanted to keep using the river to transport needed supplies; the Union wanted to stop this supply route and drive a wedge that would divide Confederate states and territories. Particularly important to the South was the stretch of the Mississippi that included the mouth of the Red River. The Red was the Confederacy's primary route for moving vital supplies between east and west: salt, cattle, and horses traveled downstream from the Trans-Mississippi West; in the opposite direction flowed men and munitions from the east.
In the spring of 1862, the Union took control of New Orleans and Memphis. To make sure it could continue to use the middle section of the river, the South fortified positions at Vicksburg, Mississippi and Port Hudson, Louisiana.