 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.