Complex sentence: He resigned the commission in May 1862 to become a brigadier general of the Missouri state militia (Union), and was appointed a brigadier general of U.S. Volunteers to rank from November 29,1862.
Split into simpler sentences: He resigned the commission in May 1862 to become a brigadier general of the Missouri State Militia (Union). He then was appointed as a brigadier general of U.S. volunteers to rank from November 29,1862.