Complex sentence: In March 2005, the prior Viacom announced plans of looking into splitting the company into two publicly traded companies because of not only a stagnating stock price but also the rivalry between Leslie Moonves and Tom Freston, longtime heads of MTV Networks.
Split into simpler sentences: In March 2005, the prior Viacom announced plans of looking into splitting the company into two publicly traded companies. The company was not only dealing with a stagnating stock price, but also the rivalry between Leslie Moonves and Tom Freston, longtime heads of MTV Networks.