The black markets could actually provide the real change that North Korea needs. Engaging in counter-economics provides elements of free trade that would greatly benefit the people of the north but would threaten foreign corporations. This is why the U.S. will take whatever excuse they can to further sanction the north.

I don't follow the logic here. Sanctions make it more difficult for Norks, both the leaders and the citizens, to acquire foreign goods, including those from the US. If opening up the North as a market for US interests were really the final goal here, sanctioning makes no sense.