Queen's Gambit Declined: Harrwitz Attack, Two Knights Defense, Blockade Line

The Queen's Gambit Declined: Harrwitz Attack, Two Knights Defense, Blockade Line is a chess opening classified under ECO code D37 in the Closed & Semi-Closed Games family, arising from 1.d4 d5, including the Queen's Gambit, Slav Defense, and related systems. It is reached after 7 moves: 1. d4 Nf6 2. c4 e6 3. Nc3 d5 4. Nf3 Be7 5. Bf4 O-O 6. e3 Nbd7 7. c5. The resulting position leaves black to move.