Complex sentence: In 1967, Atlantic Records was sold to Warner Bros.-Seven Arts, activating a "key man" clause (which Jim Stewart had insisted upon) in the Stax/Atlantic distribution contract.
Split into simpler sentences: In 1967, Atlantic Records was sold to Warner Bros.-Seven Arts. The sale of Atlantic to Warner activated a "key man" clause (which Jim Stewart had insisted upon) in the Stax/Atlantic distribution contract.