Blackmar-Diemer Gambit Declined: O'Kelly Defense

In the Blackmar-Diemer Gambit Declined: O'Kelly Defense, the white player starts with d4 to gain central control of the board. This move instantly puts pressure on the black pawn at d5, forcing it to defend or capture. By controlling the center, white can set up their pieces for more aggressive attacks. Additionally, this move may lead to the Blackmar-Diemer Gambit, where white sacrifices the e4 pawn for a swift development and a lead in piece activity.

Black playing d5 in response to white's d4 move aims to gain control of the center of the board. This move challenges white's central pawn and restricts the movement of their light-squared bishop. Moreover, it's a solid pawn structure that allows black to develop pieces and supports the control of the board. By controlling the center of the board, black can thwart white's aggressive attacks and have more strategic options.

In response to Black's d5 move, white's e4 move challenges black's control of the center of the board. It also offers white an opportunity to open up their pieces and exploit their lead in piece development. Moreover, the move attacks the black pawn at d5, forcing it to defend or capture. If black captures the pawn, then white can follow up with the Nc3 move which indirectly attacks the black knight and threatens to recapture the pawn, regaining control of the center.

In the Blackmar-Diemer Gambit Declined: O'Kelly Defense, black opts to capture white's pawn at e4 with their pawn at d5. This move frees black's queen and bishop, allowing them to deploy and contest control of the board. Furthermore, this pawn break can create more space for black's minor pieces to maneuver. Black capturing the pawn may also force white's knight to retreat to b1, where it is less active and takes away control of the center. However, black may have to be prepared to deal with an onslaught of white's pieces in the middle game if they haven't prepared their defenses properly.

In response to black's capture of the pawn at e4, white plays Nc3 to control the center of the board and support the pawn at d4. The knight also indirectly attacks the black pawn at e4, forcing it to move or be defended. Additionally, the Nc3 move opens up the possibility of aggressive attacks in the upcoming moves. For instance, white may follow up with the f3 move, establishing a pawn center and preparing to castle on the king's side. The Nc3 move also develops white's knight and frees up a square for the light-squared bishop to be deployed in the future.

In response to white's Nc3 move, black plays Nf6 to develop a knight and contest control of the center of the board. The move also indirectly protects the black pawn at d5, which is currently attacked by white's knight. Additionally, by playing Nf6, black threatens to capture white's pawn at e4, which may be advantageous as the pawn controls an important central square. Moreover, the knight at f6 provides support to the pawn at e5 if black opts to play it in the future, potentially opening up a diagonal for black's light-squared bishop.

In the Blackmar-Diemer Gambit Declined: O'Kelly Defense, after the Nf6 move, white plays f3 to solidify their pawn center and prevent black's knight from attacking the e4 pawn. Additionally, this pawn move prepares the castling of white's king on the kingside and maintains control over the e4 square. White may also play Bd3 after f3, deploying their bishop to an active diagonal. However, playing f3 also comes with a weakness in white's pawn structure and black may have opportunities to exploit this weakness in the later stages of the game.

In response to white's f3 move, black plays c6 to control the d5 square, restrict white's pawn push to d5, and support their pawn at d5. This also prevents the possibility of white's pawn storm on the kingside and provides an escape square for the black knight on b8, if needed. Additionally, the pawn break at c6 may help black gain space and push white's pieces back. However, by playing c6, black might lose some flexibility in developing their pieces, especially their bishop at c8 and their knight on b8. Moreover, the pawn move weakens the b6 and d6 squares which may be exploited by white in the middle game.