Image caption Kim Jong-un (right) was chosen as his father's successor last year

The death of Kim Jong-il is the ultimate moment of truth for North Korea.

This strangest of regimes has survived for 20 years after most forms of communism elsewhere either perished or morphed into something more sensible. So we had best not underestimate its staying power.

More particularly, North Korea has already successfully managed the world's first dynastic transition in a notionally communist regime.

That was when Kim Jong-il succeeded his own father - the regime's founder, self-styled Great Leader Kim Il-sung - back in 1994.

Can they bring it off again? The difference is that Kim Jong-un, though swiftly named as Great Successor, is a callow 20-something of no known experience or confirmed opinions.

Kim Il-sung groomed Kim Jong-il as successor for 30 years. Kim Jong-un, by contrast, has had two years at most to prepare for the ruling role he is now suddenly plunged into.

He inherits a poisoned chalice. This untried youth must now run a country both at odds with most of the world and oppressive of its long-suffering people - who may not obey forever, despite the remarkable scenes of publicly orchestrated grief which we are now witnessing.

Behind the mask

So what will happen? The rest of us can only watch and wait. Will Kim Jong-un succeed as successor? At best he can be little more than a figurehead - but for whom and what, exactly?

North Korea runs a famously tight ship and is adept at putting on a good show. But behind the mask of unity lurk bitter rivalries and tough choices. These are of at least four kinds.

First, personalities. Kim Jong-un's elder half-brother Kim Jong-nam was passed over for the succession. He lives in China, which means he has Beijing's protection.

In case Jong-un is not up to the job, his big brother - a known reformer - might yet have a role to play. And in Pyongyang itself there are further personal and family rivalries, though details are murky.

Second, there are institutional rivalries. Three bureaucracies - the Party (WPK), the military (KPA) and the Cabinet - vie for power, and may not see eye to eye on how to proceed.

Under Kim Jong-il, the Party had largely withered while the KPA flourished, until last year's public launch of Kim Jong-un at the first WPK delegates' meeting for more than 40 years.

Less powerful than either the party or army, technocrats in the Cabinet yearn for economic reform to arrest North Korea's decline into poverty. This is the third issue: policy choices.

Image caption Mr Kim's father Kim Il-sung is still revered as the "Eternal Leader"

Patently North Korea is on the road to nowhere, refusing reform and in its nuclear defiance. Yet there is no guarantee that it will change on either front, due to military vested interests.

Or a mix is possible: partial market reform while clinging to nuclear weapons. China could live with that. But for South Korea, the US and Japan, this would create dilemmas.

Which brings us to the fourth dimension. How will political succession in North Korea play out in regard to other powers, above all South Korea, China, the US and Japan?

For now all of these must be mainly spectators, vigilantly watching whatever might unfold in Pyongyang. Importantly, while all are involved in the stalled nuclear six-party talks (as is Russia), this does not mean that their interests are identical.

South Korea faces two elections next year. President Lee Myung-bak cannot run again. His conservative ruling Grand National Party is currently on the back foot, for several reasons.

One has a sense that Mr Lee's hardline approach - reversing the "sunshine policy" of engagement, which Seoul pursued for a decade until 2007 - has not made the South safer. As witnessed by the North's two fatal attacks on the South last year, sinking a warship and shelling an island.

Those assaults were widely regarded as linked to Kim Jong-un's rise: the "young general" showing his mettle.

One fear now is that he may again try a similar provocation. In that case Seoul would feel bound to retaliate, with the risk that conflict could escalate out of control.

More broadly, Seoul's self-inflicted loss of influence in Pyongyang has been Beijing's gain.

Influence

A year ago, a diplomatic cable leaked by the Wikileaks website suggested that China would accept a Korea reunified under the South. But that was sheer wishful thinking and self-deception in Seoul.

The truth is the opposite. A plethora of new military, political and business links show that China has taken a strategic decision to grit its teeth and prop up North Korea, come what may. The reclusive Kim Jong-il visited China four times in the last 20 months of his life.

Beijing would like Pyongyang to reform its economy and ideally give up nuclear weapons but it may insist on the former more than the latter. Unlike Seoul, it will not throw away the influence it has painstakingly built up over this most difficult of regimes.

North Korea for its part mistrusts China, as it mistrusts everyone, but it needs protection, and right now China is its protector. (Russia may play such a role, but has much less influence.)

Also largely bereft of influence are South Korea's major allies. Japan, beset by its own woes and obsessed by just one of the Kim dynasty's many crimes - its abduction of a number of Japanese citizens in the 1970s and 1980s - no longer even trades with North Korea.

Image caption There are fears that military tensions on the peninsula could escalate

Tokyo has no clout at all in Pyongyang now, and can only watch nervously whatever unfolds there.

The same applies to the global superpower. Barack Obama's policy of so-called "strategic patience" - ie doing nothing much - means that Washington cannot sway events in North Korea.

Fitful dialogue over the past three years has made no real progress on any front.

As ever the main US concern is nuclear. With Kim Jong-il gone, whose finger will now be on North Korea's red button? Might they be trigger-happy or nervously miscalculate?

In that case artillery or missile launches are likelier, thankfully. A third nuclear test cannot be ruled out, just to warn the West not to meddle as they did in Libya.

The nightmare scenario is "loose nukes" if an overt power struggle were to break out in Pyongyang. In that case, South Korea and its US ally have contingency plans to intervene.

But so does China - separately. The nightmare of nightmares would be if an already fraught political transition were to escalate into a confrontation between rival superpowers.

The US and China fought a hot war in Korea before, in 1950-53. Once is more than enough.

The hope must be that Kim Jong-un, or whoever, will mend at least some fences and start to bring North Korea in from the cold. But there are no guarantees. This is an anxious moment.