Queen's Gambit Declined: Vienna Variation

The opening move of d4 by White is a classic example of a central pawn move aimed at controlling key squares on the board and opening lines for the pieces. This move also creates an immediate threat to Black's e5 pawn and puts pressure on the center of the board. By playing d4, White hopes to gain control of the center and gain an advantage in the game. The move also allows for the possibility of developing the Queen's Knight to c3, putting additional pressure on Black's center.

Black's move Nf6 is aimed at challenging White's control over the center of the board. By bringing the Knight out early, Black threatens to attack White's central pawn at d4, which can disrupt White's plans. This move also prepares for the eventual development of Black's other pieces, particularly the Queen's Bishop to e7, which supports the d5 pawn. Additionally, the Knight can be used to control key squares on the board, such as e4 and g4, limiting White's opportunities for further advancement.

White's move c4 is a classic example of a central pawn move aimed at further controlling the key squares in the center of the board. By playing c4, White creates additional threats to Black's center and limits Black's options for developing their pieces. This move also prepares for the eventual development of White's Queen's Knight to c3, which can put further pressure on Black's central pawns. Additionally, the move can create opportunities for White to open up lines for the Queen's Bishop and Queen, potentially leading to an attack on Black's castled King.

In the Queen's Gambit Declined: Vienna Variation, Black's move e6 is a solid response aimed at reinforcing their control over the central d5 square. By playing e6, Black supports the d5 pawn and prepares to develop the Queen's Bishop to e7, completing Black's control of the center. Additionally, the move limits White's options for advancing their central pawns and can prepare for the eventual development of Black's King's Knight to f6. The move also prepares for the possibility of castling Queen's side, creating additional defensive options for Black's King.

White's move Nf3 is a natural and flexible development move that aims to support the central pawn at d4, reinforce control over the e5 square and prepare for possible attacks in the center of the board. By developing the Knight to f3, White also prepares for the eventual development of the King's Knight to g2, supporting the castled King's pawns. The move Nf3 also allows White to potentially threaten Black's center with a pawn advance to either d5 or e4, depending on Black's future moves. Additionally, the Knight on f3 is well placed to control important squares on the board, limiting Black's pieces' mobility and attacking options.

Black's move d5 is a common and sound way to assert control over the center of the board. By playing d5, Black immediately challenges White's central pawn at d4 and creates opportunities to develop their own pieces more effectively. The move also frees Black's Bishop on f8, allowing it to be developed more easily. The pawn at d5 also creates the potential for an eventual pawn exchange, opening up lines on the board and potentially weakening White's pawn structure. Furthermore, playing d5 threatens the Knight on f3, which might have to be moved, spending valuable time in White's development.

In the Queen's Gambit Declined: Vienna Variation, White's move Bg5 is a classic way to apply pressure to the black's e6 pawn and potentially force a pawn weakness or tactical opportunities. The move pins Black's Knight and can lead to the exchange of this piece, making Black's development more difficult. Furthermore, this move creates additional pressure on Black's position, potentially forcing the placement of their Bishop to d6 instead of its more natural square, e7. Bg5 also prepares for the eventual castle of the White's King's side and reinforces control over the central dark squares. Additionally, this Bishop can also be used to support possible pawn advances and attacks.

Black's move Bb4+ is an aggressive way to put pressure on White's position and gain control of the center of the board. By developing the Bishop to b4, Black attacks White's Knight on f3, potentially forcing its removal. The move also supports Black's control over the central d4 square and limits White's ability to further develop their pieces. Additionally, the move can force White's King to move, preventing or delaying short-term castle moves. Bb4+ also creates the possibility of exchanging the dark-squared Bishops, which can be advantageous for Black's long-term strategy. In sum, this move is an aggressive attempt by Black to disrupt White's position and gain control of the board.