Complex sentence: After graduating from Miami University in 1860, Harris enlisted as a private in the Union Army, and quickly rose to the rank of Colonel of the 75th Ohio Infantry, seeing action in many of the Army of the Potomac's engagements.
Split into simpler sentences: After graduating from Miami University in 1860, Harris enlisted as a private in the Union Army. Hw quickly rose to the rank of Colonel of the 75th Ohio Infantry, seeing action in many of the Army of the Potomac's engagements.