French Defense: St. George Defense, Sanky-George Gambit

The French Defense is a common opening played by black in response to the move 1.e4 by white. In this opening, black aims to control the center of the board with pawns and pieces. White's move e4 on the first turn is an attempt to gain control of the center as well. White's position will be stronger if they can control more space in the center. By occupying the e4-square with a pawn, white prevents black's pawn from advancing and occupying that space.

Black's move e6 on the second turn aims to control the d5-square. By placing a pawn on e6, black prepares to push their pawn to d5, which would undermine white's pawn on e4 and potentially open the way for black's light-squared bishop to become more active. It can also secure black's knight on f6 by blocking potential attacks from white's pawns. In sum, e6 is a common move in many openings played by black to control central squares and set up favorable pawn structures.

White's move d4 on the third turn aims to gain control of the center and threaten to capture black's e6 pawn. By pushing the d-pawn, white gains more space in the center and opens lines for their bishop and queen. This move also puts pressure on black's central pawns and can potentially lead to an open center, which may favor white's development and attacking chances. In sum, d4 is a typical move in many openings played by white to control central squares and challenge black's position.

In the French Defense: St. George Defense, Sanky-George Gambit, Black's move a6 on the third turn aims to prevent white's knight from entering the b5 square and harassing black's pawn on c7. By playing a6, black can restrict white's pieces and limit their attacking options. Additionally, this move can ultimately prepare for b5, which would challenge white's pawn on c4 and create counterplay on the queenside. In sum, a6 is a useful move in the French Defense to secure the b5-square and potentially take control of the center.

White's move c4 on the third turn expands their control of the center and puts pressure on black's pawn on d5. This move is also known as the "Queen's Gambit pawn advance" and may transition into a different opening if black accepts the gambit by capturing on c4. By playing c4, white can develop their queen's bishop and potentially open up lines for their queen and rooks. Additionally, this move can limit black's mobility on the queenside and potentially lead to opening up space for white's pieces to maneuver. In sum, c4 is a forward move by white that seeks to expand their position and challenge black.

Black's move b5 on the fourth turn aims to strike at white's pawn on c4 and potentially gain control of the center. By playing b5, black challenges white's pawn structure and creates counterplay on the queenside. This move can also prepare for the development of the c8 bishop and potentially open up lines for black's pieces. Additionally, b5 can limit white's mobility on the queenside and potentially give black more space for their pieces to maneuver. In sum, b5 is a natural response by black to combat white's early expansion in the center and seek counterplay.