Maus served as aide to Gen. Nelson Appleton Miles during the latter's inspection tour to Europe in 1897 and during the Spanish–American War in 1898. Maus was promoted to Major in June 1899 and a month later was made Inspector General of the Department of California and Columbia. He was promoted to Lieutenant Colonel in June 1902 and during 1902–03 accompanied Miles on a world tour. In January 1904 he became commander and Colonel of the 20th U.S. Infantry, which he commanded in the Philippine Insurrection until 1906, when he returned to California. He was temporarily in command of the Division of the Pacific during the absence of Gen. Frederick Funston and played an important role in maintaining order in San Francisco following the San Francisco earthquake. Maus was promoted to Brigadier General in 1906, commanding the Department of Columbia until 1911, when he was given command of a brigade of the 2nd Division in San Antonio, Texas. At his retirement in August 1913, he was commander of a brigade of the 1st Division at Albany, New York.