Chess Opening Theory/1. d4/1...d5/2. c4/2...c6/3. Nf3/3...Nf6/4. Nc3

= Slav Defence after 4.Nc3 = Moves: 1. d4 d5 2. c4 c6 3. Nf3 Nf6 4. Nc3

White develops his other knight onto the c3 square where it increases the pressure on d5 and also exerts control over the e4 square. Although this knight is sometimes developed onto the d2 square by Nbd2, the c3 square is probably slightly preferable since it does not block in white's bishop on c1.

Theory table
1.d4 d5 2.c4 c6 3.Nf3 Nf6 4.Nc3