On Jan. 6, in a man-made tunnel built on the country's east coast, North Korea conducted its fourth nuclear test. It was yet another dubious milestone for the isolated, impoverished country.

North Korea has gained a reputation for the strange and unusual, and perhaps the strangest of all is its nuclear program. Why did such a small, impoverished country decide to build nuclear weapons? How many does it have and how does it plan to use them? What does the new test mean? How are the country's neighbors responding?

North Korea has a long tradition of being an outlaw state, provoking neighbors since the 1960s and using its status as a Soviet client state as a shield against retribution. But the Soviet Union collapsed in 1991, leaving the country without a powerful benefactor.

Even worse, in 1991 Pyongyang watched in dismay as the U.S. military easily destroyed the Iraqi military — a military that in weapons and numbers looked a lot like the North Korean People's Army. The lesson was clear: The country's large conventional forces could no longer protect the regime.

The impoverished country — with a GDP one third of Ethiopia's — poured resources into a nuclear program and in 2006 detonated its first nuclear bomb.

It worked. Nuclear weapons have become the regime's trump card, giving Pyongyang's neighbors — and the United States — a strong disincentive to punish the regime for one violent provocation after another. The country's nuclear weapons have become the new shield against retribution, ensuring the survival of the regime.

North Korea has tested nukes four times, starting in 2006, in underground tunnels located in the eastern half of the country. The largest weapon tested so far had half the explosive power of the bomb dropped on Hiroshima.

At the same time, the size of the country's nuclear arsenal is set to ramp up dramatically. North Korea is estimated to possess between 10 and 16 nuclear weapons, and under the best-case scenario could have up to 100 weapons by 2020.

Pyongyang has stated that the bomb detonated on January 6 was a "Hydrogen bomb." Hydrogen bombs are nuclear weapons that add a hydrogen fusion reaction, producing a vastly more power bomb. Ordinary nuclear weapons are generally measured in the kilotons, or thousands of tons of TNT in explosive power; H-bombs are are generally measured in megatons, or millions of tons of TNT.

Alternately, Hydrogen bombs may refer to ordinary nuclear weapons boosted with hydrogen isotopes to increase their destructive power. While still nowhere near the power of a real H-bomb, the bombs are easier to design and produce. This is a far likelier scenario for what North Korea produced.

At the same time, North Korea is working on missiles to deliver its nukes. The U.S.-Korea institute at Johns Hopkins University has assessed Pyongyang as being able to put a bomb on its medium and intermediate-range nuclear missiles. These missiles could strike neighboring countries including Russia, China, South Korea, Japan, and U.S. military bases in the Asia-Pacific region.

The big question is whether North Korea could strike the United States. North Korea has demonstrated missile technology that theoretically has the range to reach Alaska. A new version of the KN-08 ballistic missile, which may be operational as early as 2021, might be able to reach the West Coast with a "lightweight" nuke.

North Korea is also developing a submarine-launched missile and a missile submarine, the Gorae ("Whale") class, to launch it. While impressive for a small country, the submarine is likely much too clunky to remain undetected by regional navies, and the missile has too short a range to threaten the United States. Regardless, the submarine has at least a chance of remaining undetected in wartime, and represents the ability of the regime to strike back even after land-based nukes — and the regime — have been destroyed.

North Korean nuclear weapons are destabilizing the region, pushing neighboring states to arm themselves. South Korea has developed a cruise missile, the Hyunmoo-3, designed to destroy North Korean missiles fueled and sitting on a launch pad. Japan is set to invest in the U.S.-made Terminal High Altitude Area Defense (THAAD) missile defense system, and there have been calls in the Japanese government for the country to produce a cruise missile of its own. It's doubtful either country would have any interest in these weapons were North Korean nukes not in the picture.

Meanwhile, across the Pacific, the United States is set on the horns of a dilemma. Sanctions and punitive economic measures by the international community failed to prevent North Korea from developing nukes. Real military action would likely trigger retaliatory attacks against America's allies, South Korea and Japan. And the prospect of the U.S. military waging war on China's doorstep will anger Beijing.

In the meantime North Korea's nuclear arsenal continues to grow, and its missiles inches closer towards the mainland U.S.A.

The question mark in all of this is China. North Korea has been a client state of China for decades. China does not approve of North Korea's nuclear program, and has taken punitive action, including canceling fuel deliveries, that have resulted in it having been branded a "turncoat and an enemy" by the Kim regime.

At the same time, China does not want a collapse of the North Korean regime, which would put millions of refugees on its border. China does not want a united Korea either, as that would almost certainly put a pro-U.S. government on its southern border. Ideally, China would like a cooperative neighbor, even if it meant accepting the Kim dynasty. But the Kims seem to have other plans.

It seems unlikely that a handful of people in a poor country such as North Korea could wield such power and stymie entire governments. And yet three generations of the Kim dynasty have done precisely that. Pyongyang's nukes are both a guarantor of the survival of the Kim dynasty and a conundrum for the international community. Neither will be going away anytime soon.