The reason for Sigel's relief is unclear. Some accounts cite failing health; others that he expressed his displeasure at the small size of his corps and asked to be relieved. Many historians also cite the lack of military prowess and skill. On multiple occasions, he made terrible military decisions, resulting in deaths of his soldiers and also Nathaniel Lyon in 1861 at the Battle of Wilson's Creek. General-in-chief Henry W. Halleck detested Sigel, and managed to keep him relegated to light duty in eastern Pennsylvania until March 1864. President Lincoln, for political reasons, directed Secretary of War Edwin M. Stanton to place Sigel in command of the new Department of West Virginia.