 Through 2005 more diplomatic talks were attempted between the United States, North Korea, South Korea, China, Japan, and Russia (the six-party talks) but little concrete change occurred.Because North Korea had not conducted a successful test of a nuclear device, the extent of its nuclear weapons program remained ambiguous through 2005 and much of 2006.Though North Korea conducted numerous missile tests (some of which were branded failures by international experts), the question of whether they had actually mastered all aspects of nuclear weapons technology – ranging from material production to complex nuclear weapon design needed to produce the final detonation – remained unanswered.