Chess Opening Theory/1. d4/1...d5/2. c4/2...c6/3. Nc3/3...dxc4/4. e4

White uses the fact that the capture has left the e4-square undefended and expends their centre, revealing an attack from the light-squared bishop on the c4 pawn.

Black generally holds onto their pawn with 4...b5, preparing to push b5-b4 if White challenges their pawn with a2-a4.

4...e5 was the first main line, but players with White have shown that it is not to be feared, scoring very well against it.

This move was popularised after being played in round 6 of the world championship rematch between Alexander Alekhine and Max Euwe,^[1] which proceeded 4...e5 5. Bxc4 exd4 6. Nf6!? (if 6...dxc3 7. Bxf7+ Ke7 with the possible continuation of 8. Qb3 Qb6? 9. Bxg8 Rxg8 10. Qxg8 ± Sarapu - Anthony Garbett 1976^[2]) 6...b5 7. Nxb5 Ba6 8. Qb3 Qe7 9. O-O Bxb5 10. Bxb5 ±. Alekhine went on to win the game.

It wasn't until 1939 that players started holding onto the c4 pawn with 4...b5.^[3]

1. d4 d5 2. c4 c6 3. Nc3 dxc4 4. e4