Complex sentence: He later became the lieutenant colonel of the 5th Michigan Cavalry and then, in the late summer of 1862, he raised and organized the 7th Michigan Cavalry and was promoted to its colonel on February 9,1863.
Split into simpler sentences: He later became the lieutenant colonel of the 5th Michigan Cavalry. Then, in the late summer of 1862, he raised and organized the 7th Michigan Cavalry and was promoted to its colonel on February 9,1863.