Chess Opening Theory/1. d4/1...Nf6/2. c4/2...g6/3. Nc3/3...Bg7/4. e4/4...d6/5. f4

= King's Indian Defence =

5. f4
The Four Pawns Attack is the most aggressive line for White in the King's Indian. White creates a massive pawn centre and has full control over the middle of the board ... for now. This is a dangerous line for Black, and if they don't play correctly, they will be knocked off the board by White's advancing army. However, if Black can survive the initial onslaught, they will have the better game since White will have many weak squares in their camp that their pawns can't defend. For this reason, the Four Pawns Attack isn't seen frequently at the highest levels of chess, although it's still very viable at the amateur level.

Theory table
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'''1. d4 Nf6 2. c4 g6 3. Nc3 Bg7 4. e4 d6 5. f4'''