White has set up a powerful pawn center. It's time for Black to counter-attack. 2...d5 is the main line and generate tension on both pawns. 2...e5 can transpose into the Scotch Game, but other continuations are also possible, either a center collapse after 3. dxe5 or a closed game after 3. d5.

1. e4 Nc6 2. d4

Wikipedia has related information at Nimzowitsch Defence.

• Kasparov, Garry, & Keene, Raymond 1989 Batsford chess openings 2. ISBN 0-8050-3409-9.