Chess Opening Theory/1. d4/1...d5/2. c4/2...e6/3. Nc3/3...Nf6/4. Nf3/4...c6/5. Bg5/5...dxc4/6. e4

6. e4
White claims the entire Center, while revealing the f1 bishop's attack on the c4 pawn. Black must fortify the c4 pawn with …b5