With 2...e6 Black plans to prevent e4 by pinning the Queen's Knight. After 3.Nc3, Black plays 3...Bb4, and will follow through with ...Bxc3 if White continues to prepare e4.
White has several good continuations, but the diagram shows one of the most popular. White abandons the plan for an early e4 and switches to rapid development of the Kingside pieces.
White can abandon the struggle for e4 a move earlier by playing 3.Nf3. After 3.Nf3, Black often continues 3...b6, preparing to develop the Queen's Bishop on b7, and bringing another piece to bear on e4. White has several good continuations, and the following is one of the most popular.
1.d4 Nf6 2.c4 e6 3.Nf3 b6 4.g3
White counters the development of Black's Bishop on the long diagonal by doing the same.
