According to the US Department of Defense and other sources, North Korea is partly surrounded by huge American military bases - with 83 in South Korea and 113 in Japan, mainly concentrated on the island of Okinawa.
"They feel threatened, that's also what I hear in my discussions with the North Koreans, since the end of the Korean War in the 1950s,” says Paul Tjia, director of GPI consultants in Rotterdam, who helps European busineses invest in North Korea.
That is a very difficult job under current circumstances and he understands why Pyongyang is acting as it does.
“They do not see any progress in the field of international economic cooperation," he says. "There are still economic sanctions, there is still no diplomatic advancement in relations between, for example, the US and North Korea and, as long as this Cold War situation continues, they have no problem in doing one or more new tests.”
North Korea usually gets diplomatic support from China and Russia, two countries it shares borders with, and it does business with these countries.
But how interesting is North Korea for Western investors?
Pyongyang has taken some initiatives and some Western entrepreneurs are looking into this.
“They are opening up the country, they are setting up a lot of what they call 'special economic zones', to attract investors,” says Tjia.
"But what they see is that the interest among foreigners, especially Europeans, is still not that high. They want to open up to the outside world but the outside world is still very reluctant to engage with the North Koreans.”
As for the nuclear test may have been motivated by more than lack of interest by foreign investors.
“It is an act to show that it is a regime that still has grip on affairs, that knows how to run the country and that is able to produce sophisticated nuclear bombs,” says Remco Breuker, a Korea specialist with Leiden University.
“And internationally, given the fact that the North Korean army has been in decline for a rather long time, it's underfed, its weapons are obsolete and its soldiers are not the most motivated in the world, having access to a nuclear bomb does work as a deterrent.”
For sure, international reactions to the latest test have been very sharp, the US calling it “provocative” and condemning the act as a “clear violation of past Security Council resolutions”. The Japanese ambassador to the UN, Motohide Yoshikawa, said the security council will take “significant measures”, without going into detail.
But the danger for Pyongyang may come from elsewhere.
“I don't understand why the North Korean regime is playing with fire," says Breuker. "I don't think it would be a stretch of the imagination to suppose that, if this goes far enough, China will sponsor a coup d'état in Pyongyang. Things like that have happened before. So it is a very dangerous game Pyongyang is playing and I am not sure what they are gaining except for regime stability."
So the tests could backfire.
"The danger is not coming from the UN, it is not coming from America or South Korea. But it might be coming from China," Breuker concludes.