North Korea made such thoroughly clandestine preparations for its fourth nuclear test that it even caught its sole real ally Beijing on the back foot.
The international community was caught mostly off guard, since North Korea watchers had not been expecting the event so soon even though some preparations were clearly going on at the test site.
But leader Kim Jong-un made no mention of nuclear weapons in his New Year's speech, so there was not even a veiled hint to go by.
The North aired a special broadcast two hours after the test Wednesday and said Kim gave the orders on Dec. 15 and the final go-ahead on Sunday.
The North's official Korean Central News Agency quoted Kim as saying on Dec. 10 that the North has now become a "powerful nuclear weapons state ready to detonate a hydrogen bomb."
Since nobody knows much, the speculation mill has gone into overdrive.
Some point out that Dec. 10 was the same day North Korea's flagship Moranbong girl band arrived in Beijing, but they canceled their concert and left soon after, possibly because Chinese officials bristled at Kim's boast.
The order to carry out the test also came five days after the death of Kim Yang-gon, a point man in negotiations with the South. Some pundits speculate that the vacuum left by his death gave military hardliners an opening to push ahead with the test.
Kim Seung at the Korea Defense Forum said hardline military brass had been engaged with a power tussle with Kim Yang-gon and his United Front Department and were angry when the department spearheaded cross-border projects following an easing of military tensions on Aug. 25.
That makes it more likely that the car accident that killed Kim Yang-gon had been arranged as a result of this power struggle, and that the unruly military is in the ascendancy again, some pundits say.
But in the official statement, North Korea only claimed that the nuclear test was conducted in response to the threat of U.S. nuclear weapons.
One diplomatic source said the test was probably an attempt to grab Washington's attention for any advantage in future negotiations.
Yet other diplomatic sources say the nuclear test was a birthday present for Kim, who turns 33 on Friday.
Other pundits say the main aim was to boost morale internally ahead of a Workers Party general assembly in April. Choi Kang at the Asan Institute for Policy Studies said, "Nuclear weapons development is Kim Jong-un's top achievement so far. That means he has done a poor job in improving the North's economy."
And Kim Jae-chun of Sogang University added, "The regime may lose a lot diplomatically, but it gains in terms of consolidating Kim's hold on power and uniting the public."
