Chess Opening Theory/1. b4/1...e6

Black pushes the e-pawn so they can gain control over the center. This move also allows the pawn to move without getting attacked by a bishop on b2. Secondly, this move attacks the pawn on b4. However, White can play 2. Bb2 anyways, as Black cannot capture with 2...Bxb4??, as it hangs a rook with 3. Bxg7!.