With his record of service in the Mexican War, Van Dorn was entered Confederate service as a colonel in March 1861, then advanced to brigadier general in June, and to major general in September. He commanded the Army of the West until he lost the Battle of Pea Ridge (Elkhorn). He was transferred to the Army of the Mississippi. His loss at Corinth led to his appointment as commander of the cavalry in the Army of the Mississippi. His achievement in December 1862 at Holly Springs, Mississippi, temporarily delayed Grant's operations against Vicksburg. Van Dorn was assassinated in his headquarters on May 7, 1863.