How Will Afghanistan “Defray” the Cost of the War?

I heard this line during Donald Trump’s Afghanistan speech tonight, but I was distracted and wasn’t quite sure what he had said. But now the transcript is available, so here it is:

In this struggle, the heaviest burden will continue to be borne by the good people of Afghanistan and their courageous armed forces. As the prime minister of Afghanistan has promised, we are going to participate in economic development to help defray the cost of this war to us.

That zipped by mighty quickly, didn’t it? Let’s rewind and pause a bit. What exactly does Trump mean? What does he plan to extract from Afghanistan to help “defray” the cost of the war?