Complex sentence: In August 1865 he was transferred to the Division of the Pacific in California, essentially in military exile until March 1869, when he was assigned to command the Military Division of the South, headquartered in Louisville, Kentucky.
Split into simpler sentences: In August 1865 he was transferred to the Division of the Pacific in California, essentially in military exile. In March 1869, he was assigned to command the Military Division of the South, headquartered in Louisville, Kentucky.