National League Division Series

In Major League Baseball, the National League Division Series (NLDS), played early to mid October, is a playoff round to determine which two National League teams play in the NLCS. It consists of two best-of-five series featuring three division winners and the winner of the wild card game.
History.
The first Division Series was played in 1981. A strike shortened the MLB season that year. Division winners from the first half took on the second-half division champions. 
The Division Series was implemented for good in 1994. The leagues were expanded two three divisions, and the wild card was also added. However, a strike cancelled the rest of the 1994 MLB season, including the playoffs. The current Division Series thus began play in 1995.