Chess Opening Theory/1. d4/1...Nf6/2. c4/2...g6/3. Nc3/3...Bg7/4. e4/4...d6/5. Nf3/5...O-O/6. Be2/6...e5

6. e5
The move e5 from Black attacks the center and gains space. The main line continues by White castling kingside to get the king away from the center, then Black plays Nc6 to gain space and develop a piece, which White immediately kicks with d5, forcing it to e7. From there, the game can branch off in several different ways.

b4 makes a pawn storm on the queenside, with the rooks developing to support in the attack. In some games, Black's kingside knight goes to h5 then back to f6 on its own volition to push the f pawn to f5 to destabilize the center and prepare g4.

Ne1 eventually rotates the knight to the center after Nd3 where it can defend better against Black's counterattack, be protected from g4as well as attack in the future,. Black's kingside knight also moves to allow f5.

Theory Table
'''1. d4 Nf6 2. c4 g6 3. Nc3 Bg7 4. e4 d6 5. Nf3 O-O 6. Be2 e5'''