Complex sentence: It was acquired by Beatrice Foods in 1955 then Leaf in 1983, then became independent again headquartered in Pittsburgh in 1996 when Hershey acquired Leaf's North American operations.
Split into simpler sentences: It was acquired by Beatrice Foods in 1955 then Leaf in 1983. It became independent again with headquarters retained in Pittsburgh in 1996 when Hershey acquired Leaf's North American operations.