Complex sentence: New York City hotel developers Robert and Laurence Tisch purchased a large stake in the Loews chain from MGM in 1959; by the summer of 1960 they had gained control of the company; the brothers became co-chairmen.
Split into simpler sentences: New York City hotel developers Robert and Laurence Tisch purchased a large stake in the Loews chain from MGM in 1959. By the summer of 1960 they had gained control of the company, and the brothers became co-chairmen.