Why did nuclear disarmament talks with North Korea undertaken between 2003 and 2009 by the U.S., Russia, China, and South Korea ultimately appear to fail?

a. As realist theory might have predicted, the major powers involved had conflicting national interests that did not allow for significant enough concessions to North Korea.
b. North Korean leaders saw their history of interaction with these countries differently than their diplomats did, as constructivist theory might have suggested.
c. Class differences between the more powerful, capitalist states and the Marxist state of North Korea drove the failure.
d. North Korea extracted aid and assistance from the other countries involved in the talks, but failed to fulfill any promises made in exchange for it.

Answer: D