As the only country to conduct nuclear tests in the last 17 years and maintain an active nuclear weapons and ballistic missile program, North Korea is a country of global concern. Its latest nuclear test highlights two truths. First, the failure to achieve nuclear disarmament within a foreseeable time frame is a constant stimulus to regimes interested in getting the bomb. Second, each fresh proliferation incident renders nuclear abolition even more distant.
North Korea is the only country to have defected from the Nuclear Non-proliferation Treaty (NPT). Its pursuit of nuclear weapons began in the 1960s, accelerated in the 1980s and led to its withdrawal from the NPT and the collapse of the 1994 Agreed Framework that had frozen Pyongyang's nuclear program. It has made repeated commitments to abandon the weapons path in return for security assurances and economic assistance, shelved its nuclear ambitions temporarily and then broken its promises serially. Its 2006, 2009 and 2013 nuclear tests drew international condemnations and U.N.-mandated sanctions.
On Jan. 6, Pyongyang claimed to have successfully tested a hydrogen bomb, which is a step up in destructive power that gives more explosive yield for a lighter weight. The 2006 and 2009 tests were plutonium-fueled; we do not know if uranium or plutonium was used in 2013. Until then Pyongyang was not believed to have mastered the technology to miniaturize warheads and make them robust enough to withstand the rigors of a ballistic missile flight trajectory (high gravity forces, vibrations, temperature extremes).