Pope's outstanding performance on the Mississippi earned him a promotion to major general, dated as of March 21, 1862. During the Siege of Corinth, he commanded the left wing of Halleck's army, but he was soon summoned to the East by Lincoln. After the collapse of Maj. Gen. George B. McClellan's Peninsula Campaign, Pope was appointed to command the Army of Virginia, assembled from scattered forces in the Shenandoah Valley and Northern Virginia. This promotion infuriated Frémont, who resigned his commission.