Indian Systems were first introduced in the 1920s, but were never used as openings in tournaments until the 1940s when Soviet Union chess players began using them. Many current World champion players now use them. Indian Systems are very unique and very important. The theory behind them is simply this: instead of attacking the center with pawns, one attacks the center with the pieces that are on the wings, i.e. fianchettos.
There are many move sequences that can produce an Indian System arrangement, and, just like Closed Games, Indian Systems often change into other openings as the game moves along. All of them are categorized as Semi-Closed Games and all of them begin with 1.d4 Nf6. This unbalanced opening arrangement helps give both players an equal opportunity to advance.
Usually, in reply to that the opening move of 1.d4 Nf6, White will move 2.c4 in order to secure more space in the middle of the board. This also gives Knight a chance to possibly move to c3 and gives the pawn a chance to possibly move to e4. Now Black has several options of how to respond to 2.c4
2 ... e6
Black may play 2...e6, which allows more development of the Bishop. Black then has the choice of entering into several Indian variations-Nimzo-Indian Defense, Queen's Indian Defense, Bogo-Indian Defense, Modern Benoni Defense, or even a transposition to Queen's Gambit Declined.
The sequence 1.d4 Nf6 2.c4 e6 3.Nc3 Bb4 is called the Nimzo-Indian Defense, an old favorite Indian opening. In this opening, Black attacks the center squares with minor pieces, trying to swap a Bishop for a Knight in order to produce doubled pawns on White's Q-side. Sometimes White plays 2.Nf3 in order to avoid this whole conflict, which leads to the Queen's Indian Defense (1.d4 Nf6 2.c4 e6 3.Nf3 b6). This defense gives Black a solid position. One can use the Bogo-Indian Defense instead, but this approach is not as popular.
In the Catalan Opening (or Catalan System), after the movements of 1.d4 Nf6 2.c4 e6 3.g3, White's goal is to fianchetto the Bishop. This approach has features of both Queen's Gambit (1.d4 d5 2.c4) and Réti Opening (1 Nf3 followed by fianchettoing of both Bishops). There are a number of methods that allow a fianchetto to the Bishop.
2 ... g6
2...g6 aims to develop the Bishop through a fianchetto and leads to Indian variations called Grünfeld Defense and King's Indian Defense.
The King's Indian Defense (1 d4 Nf6 2 c4 g6 3 Nc3 Bg7) is another old favorite that is used even at the highest levels of chess competition because of how forceful, yet risky, it is. Grünfeld Defense (1 d4 Nf6 2 c4 g6 3 Nc3 d5) differs from King's Indian Defense only by the move d5. This defense is also very popular among World Champions.
2 ... c5
2...c5 produces an opening called the Modern Benoni Indian Defense (1.d4 Nf6 2.c4 c5).
In this movement, Black allows White to create a stronghold at d5 as well as gain control of the center with his pawns. It is risky business, but if Black moves his pieces wisely, it ends up making for a dramatic game. Some of the risk can be avoided by playing 2...e6 and then 2.c5.
Another variation is the Benko Gambit (or Volga Gambit), which is 1.d4 Nf6 2.c4 c5 3.d5 b5. In this opening Black's gambit aims to open lines in the Q-side, and White usually does not accept the offer.
Others
Other Indian systems include Old Indian Defense, Black Knights' Tango (Mexican Defense), Blumenfeld Gambit, Döry Defense, Accelerated Queen's Indian Defense, and Slav-Indian Defense. Anti-Indian combinations for White include Budapest Defense, Neo-Indian Attack, Torre Attack, and Trompowski Attack.
Indian Systems are listed under a variety of ECO codes; A45 to A79, D70 to D99, and E00 to E99.
