Complex sentence: While the Cherokee became the only nation of the Five Civilized Tribes to abolish slavery during the war, few slaves were freed as Cherokee loyal to the Confederacy held more slaves than pro-Union Cherokee.
Split into simpler sentences: While the Cherokee became the only nation of the Five Civilized Tribes to abolish slavery during the war, few slaves were freed. In fact, Cherokee loyal to the Confederacy held more slaves than did pro-Union Cherokee.