Before 1969, the National League champion (the”pennant winner”) was determined by the very best win-loss record in the conclusion of their regular season. There were four ad hoc three-game playoff series as a result of ties under this formula (in 1946, 1951, 1959, and 1962). (The American League needed to solve a tie in 1948, however, used a single-game playoff.)
A structured postseason series started in 1969, when both the National and American Leagues were reorganized into two divisions each, East and West. The two division winners in each league played each other in a best-of-five show to ascertain who would advance to the World Series. In 1985, the structure changed to best-of-seven.
The NLCS and ALCS, because the expansion to seven games, are always played at two –3–2 format: matches 1, 2, 6, and 7 are played at the arena of the group that has home field advantage, and games 3, 4, and 5 are played at the arena of the team that does not. Home field advantage is given to the team that has the better album, with the exception that the team that produced the postseason since the Wild Card can’t get home field edge. From 1969 to 1993, home field advantage was alternated between branches each year no matter regular season record and from 1995 to 1997 home field advantage was specified prior to the year.
Back in 1981, a divisional show was held due to a split season caused by a players’ strike.
Back in 1994, the team was restructured into three divisions, with the three division winners and a wild-card team progressing to a best-of-five postseason round, the National League Division Series (NLDS). The winners of the round advance to the best-of-seven NLCS.
The Milwaukee Brewers, an American League team between 1969 and 1997, and the Houston Astros, a National League group between 1962 and 2012, are the sole franchises to play in both the ALCS and NLCS. The Astros will be the only team to have won both an NLCS (2005) and also an ALCS (2017). The Astros created four NLCS appearances before going into the AL in 2013. Every existing National League franchise has emerged in the NLCS.