Aron Nimzowitsch was a central figure in popularising the Nimzo-Indian, although he was not the first player to reach its positions. The opening reflects a concern associated with hypermodern chess: controlling important central squares through pieces before committing central pawns. After 1.d4 Nf6 2.c4 e6 3.Nc3 Bb4, Black develops with a specific purpose rather than immediately copying White's pawn occupation.
The bishop pins the c3 knight against the king. Because that knight helps support e4, the pin affects White's ability to build a broad centre. Black may later exchange on c3, potentially altering White's pawns and giving up the bishop pair. That exchange is a strategic decision with benefits and costs, not an automatic instruction whenever the bishop reaches b4.
White has several ways to answer the problem. The Rubinstein develops with e3; Classical Qc2 systems address the possible exchange differently; more ambitious pawn moves create other structures. Black's centre can also change through ...d5 or ...c5. A good understanding of the Nimzo therefore combines the pinning idea with the resulting pawn arrangements.
Practise the Rubinstein main line and watch the moment when Black decides whether to exchange the bishop. Ask what White receives in return and whether Black can attack any resulting weaknesses. Nimzowitsch's opening is a useful lesson in trading one kind of advantage for another: central restraint, structure and piece activity must be assessed together.
Try this at the board
Explain how the pin on c3 changes the support for e4, then consider what White gains if Black exchanges the bishop.