Asboth remained in the United States and joined the
Union Army. Starting in July 1861, he served as chief of staff for General
John C. Frémont. Asboth was nominated
brigadier general by President
Abraham Lincoln on December 26, 1861, and the U.S. Senate confirmed the promotion on March 24, 1862, as the President did not formally make the appointment until March 22, 1862. Asboth was assigned command of the 4th Division in Frémont's western campaign. Asboth later led a division under
Samuel Curtis, and during the Arkansas campaign he occupied
Bentonville and
Fayetteville. He participated in the
Battle of Pea Ridge, leading troops at the Little Sugar Creek position. His right arm was fractured by a musket ball while bringing reinforcements to support Colonel
Eugene A. Carr. Reinforcements were transferred to
Henry Halleck from the Army of the Southwest and during the
Siege of Corinth, Asboth commanded a brigade in the
Army of the Mississippi. On January 13, 1866, President
Andrew Johnson nominated Asboth for the award of the
brevet grade of
major general to rank from March 13, 1865, and the U.S. Senate confirmed the award on March 12, 1866. ==Later life and death==