In Major League Baseball, the National League Championship Series (NLCS) determines who wins the National League pennant and advances to baseball's championship, the World Series, facing the winner of the American League Championship Series. Prior to 1969, the National League Champion (the "Pennant Winner") was determined by the best won-loss record at the end of the regular season. There was an occasional ad hoc playoff series due to ties under this formulation, as also happened in the American League. In 1981, a divisional series was held due to split-season caused by strike action.