This intermediate move leaves Black unable to defend both flanks. There followed:

with the decisive threat of 19 Rg7+.

Initiating a typical minority attack.

3.a3 b4 4.axb4 axb4 5.Qd1 was a lesser evil, getting rid of the potentially weak a-pawn.

An ugly place for the knight.

5.cxb4 Bxb4 6.Bxf6 gxf6 7.h5 offered more resistance.

Now White is doomed on the queenside.

Initiating a majority attack to soften up Black's kingside.

White adds an extra pawn to his other advantages.