Complex sentence: The Old Meijin was the same tournament as the current Meijin, but is called the "Old Mejin" because before 1976, the tournament was hosted by Yomiuri Shimbun.
Split into simpler sentences: The Old Meijin was the same tournament as the current Meijin. The reason it is called the "Old Mejin" is because before 1976, the Meijin tournament was hosted by Yomiuri Shimbun.