Complex sentence: Much of the violence was ordered around the Ku Klux Klan (KKK), a secret vigilante organization, which led to federal intervention by President Ulysses S. Grant in 1871 that suppressed the Klan.
Split into simpler sentences: Much of the violence was carried out by members of the Ku Klux Klan (KKK), a secret vigilante organization. This led to federal intervention by President Ulysses S. Grant in 1871 that suppressed the Klan.