Complex sentence: As the nucleus of his revived Klan, Simmons organized a group of men including many of the Knights of Mary Phagan, in addition to two elderly men who had been members of the original Klan.
Split into simpler sentences: As the nucleus of his revived Klan, Simmons organized a group of men. This included many of the Knights of Mary Phagan, in addition to two elderly men who had been members of the original Klan.