Since an early e4 is not likely, the battle for control of the center shifts from e4 to c4.
In most games opened with 1.d4, White plays an early c4 followed by Nc3.
Black also keeps an eye on the possibility to play ...c5 followed by ...Nc6, but has a harder time carrying out the plan.
After 1.d4 d5, most games continue 2.c4, for the reasons just discussed.
Now Black has the choice of several good moves.
Let's look at each one.
First, why not just capture the c-Pawn with
2...dxc4?
This appears to win a Pawn, but Black can't keep it.
One straightforward continuation is
1.d4 d5 2.c4 dxc4 3.e3 b5 4.a4 c6 5.axb5 cxb5 6.Qf3
where Black pays a heavy price for greed.
In all similar lines White undermines the Black pawn structure with a4 and, if necessary, b3.
Black should not play to keep the extra Pawn, but to let White recapture it with the Bishop.
Then Black can harass the Bishop on c4 with Pawns.
The diagram shows a typical continuation.
White leads in development. Black will play ...b5 and develop the Queen's Bishop on the a8-h1 diagonal.
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