Why was control of Texas important to both confederacy and the union? Which side controlled Texas during the Civil War?

Texas declared its secession from the Union on February 1, 1861, and joined the Confederate States on March 2, 1861, after it replaced its governor, Sam Houston, when he refused to take an oath of allegiance to the Confederacy. As with those of other States, the Declaration was not recognized by the United States government at Washington. Some Texan military units fought in the Civil War east of the Mississippi River, but Texas was most useful for supplying soldiers and horses for Confederate forces. Texas' supply role lasted until mid-1863, after which time Union gunboats controlled the Mississippi River, making large transfers of men, horses or cattle impossible. Some cotton was sold in Mexico, but most of the crop became useless because of the Union naval blockade of Galveston, Houston, and other ports.