Analysis

In 1950, the North Korean regime -- proclaimed two years earlier after the partition of the peninsula into US and Soviet zones -- invaded South Korea. It was beaten back by a US-led UN coalition, but Chinese intervention saved the Northern regime. Four million died. Both Koreas were devastated.

The 1953 armistice (there is still no peace treaty) left the earlier inter-Korean boundary little changed. Now called the 'Demilitarized Zone' (DMZ), it is the world's most heavily armed border.

Despite skirmishes, the peninsula has known peace for 64 years, thanks to strong US deterrence which until 1991 included nuclear weapons. The newly expanded US forces headquarters at Camp Humphreys in Pyeongtaek south of Seoul is the largest US military base worldwide, demonstrating long-term commitment.

Pyongyang's hostility to South Korea is unrelenting. Even in the 'sunshine' decade of engagement (1998-2007), it made no military concessions.

Nuclear breakout

Since the 1990s, Pyongyang's pursuit of nuclear weapons and ballistic missiles has outwitted all efforts to stop it, from the 1994 Agreed Framework to the China-hosted Six Party Talks (2003-08).

Under Kim Jong-un, supreme leader since 2011, both programmes have accelerated, with fewer failures. The two latest missiles, launched last month, appear to be intercontinental ballistic missiles (ICBMs), potentially able to strike the continental United States. US intelligence reportedly now believes that North Korea can miniaturise a nuclear warhead, another major step towards building a viable nuclear-armed ICBM (see NORTH KOREA/US: Washington will prove a paper tiger - July 12, 2017).

Pyongyang's motives

The Kim regime's quest for weapons of mass destruction (WMD) has several motives.

North Korea has always been ultra-militarised, with the world's fourth-largest armed forces. Outspent and outgunned by the far richer South, it sees WMD and other asymmetric warfare as levelling the playing field and indispensable for self-defence.

The fates of Saddam Hussein and Muammar al-Qadhafi reinforced the view that only WMD could save North Korea's leaders from a similar fate.

WMD were also a potential bargaining chip, as seen by the Agreed Framework and Six Party Talks, although Pyongyang proved persistently mendacious and evasive.

North Korea's new regime

Where his predecessors at least feigned readiness to negotiate, Kim Jong-un has written North Korea's nuclear status into the country's constitution.

Pitched into power with little preparation and potentially vulnerable to a military coup, Kim arguably had little option but to show toughness and loyalty to his father and grandfather by reaffirming and reinforcing their signature WMD programmes.

His relentless forging ahead with missile tests, regardless of the crisis this creates, may confirm reports that he is hot-headed.

Trump takes over

Kim Jong-un now faces a US president unlike any predecessor. Trump's gnomic tweet that a North Korean ICBM "won't happen" and his administration's refusal to rule out military options unnerve Washington's regional allies in South Korea and Japan, who are in the front line.

Different administration figures send mixed signals. Secretary of State Tillerson recently insisted that Washington does not seek regime change. This contradicted remarks by CIA director Mike Pompeo. Then National Security Adviser General HR McMaster said on August 7 that it is "intolerable" to Trump for Pyongyang to have nuclear weapons that can threaten the United States, saying that "We have to provide... a military option".

Potential triggers for conflict

Risk is therefore growing. Either side may misread the other's plans or dig themselves into a rhetorical redoubt rendering retreat impossible.

In such an atmosphere, small incidents or fear alone, which in calmer times could be contained, might escalate into armed conflict. The following are among the potential triggers.

Trigger 1: Rogue missile

Though the trend is towards growing accuracy, a North Korean missile test gone awry might accidentally hit South Korea or Japan, or an aircraft.

On August 3, Air France-KLM expanded its no-fly zone near North Korea after one of its planes passed within 100 kilometres of the ICBM launched on July 28. Since Pyongyang gives no warning of its launches, aircraft and shipping are potentially at risk.

Accidental strikes are not solely a North Korean issue. In July 2016, a Taiwanese warship inadvertently launched a missile 40 nautical miles into the Taiwan Strait. It did not reach Chinese territory but hit a fishing boat, killing its captain. In the context of the heavily armed inter-Korean border, a similar mishap could have severe consequences.

In either case, establishing that an accident was not an attack would be difficult.

Trigger 2: Missile interception

With missile defence an abiding concern and major investment, many in Washington would welcome a test of actual capability to destroy a North Korean missile in flight during a test. Pyongyang could construe this as an attack.

Trigger 3: US pre-emptive strike

Since the chances of hitting a lofted ICBM are uncertain, some US hawks would rather strike weapons or facilities on the ground before North Korea can use them. One suggestion is Mayang-do naval base, where North Korea's submarine programme is concentrated.

Trigger 4: Border clashes

North Korea intermittently causes incidents along the border:

• In 2010, it sank the South Korean corvette Cheonan and shelled a South Korean base on Yeonpyeong island, causing 46 and four deaths respectively.
• In 2015, newly laid North Korean mines maimed two South Korean soldiers.
• That led to a cross-border exchange of fire; both sides shot at hills, well away from human or military targets. Such restraint might not hold in a wider crisis.

Trigger 5: Cyberattack

It is possible that North Korea now has the ability to launch cyberattacks that inflict large-scale economic costs and even fatalities.

North Korea might launch a cyberattack to test its capabilities or as a limited form of escalation or tension-building measure, but the attack may be more damaging than anticipated.

The target country's government would face pressure to retaliate proportionately. However, North Korea is highly resistant to cyberattacks because its ICT systems are so isolated from the global internet, so physical retaliation may be used.

Trigger 6: Regime collapse

If Kim Jong-un were deposed or a regiment rebelled, not only South Korea and its US ally but also China might well intervene to ward off threats and pursue their preferred outcomes.

Situational factors

The above scenarios might be more or less rapidly contained, or, more plausibly, escalate to varying extents. The following recent developments increase the risk.

Since Pyongyang cut trans-DMZ hotlines and Seoul under President Park Geun-hye forswore secret contacts, there are no longer any known inter-Korean channels of communication, except at the Panmunjom truce village.

Kim Jong-un has rebuffed outreach by South Korea's new president, Moon Jae-in, as "insincere". Moon is torn between hopes of resuming inter-Korean dialogue and fears of being portrayed as soft on the North (see SOUTH KOREA: New leader faces pressures on all sides - May 17, 2017). Early indications suggest the latter will trump the former.

Degrees of escalation

Level 1: Limited violence

Limited violence confined to border areas might be quickly contained, as it has since 1953, thanks to allied restraint.

However, after 2015's mine and shooting incidents, South Korean forces loosened their rules of engagement to permit swifter resort to kinetic responses.

Moreover, in the past Washington often stayed Seoul's hand, but Washington itself may now be less restrained in responding to any Northern aggression.

Level 2: One-off gamble

One side might launch a major but one-off strike, gambling on a similarly limited response. US forces might bomb North Korea's naval base in Sinpo, or North Korea may again strike a Southern island near its coast. Some in Tokyo fear that Japan is a tempting target for North Korea since neither China nor many South Koreans have much affection for the country so their response would be less severe.

It is doubtful that a one-off strike could in practice be prevented from escalating. In the current climate, whichever side was hit would certainly retaliate.

Level 3: Artillery and aerial bombardment

If US forces bomb Pyongyang or North Korean artillery pounds Seoul, even if these are partial strikes (say on a single suburb), civilian casualties would be in the tens of thousands. Outrage and fear of pre-emption would likely lead to further escalation.

At 513 persons per square kilometre, South Korea has the world's third-highest population density (city-states and islands excluded). Greater Seoul, almost all of which is within 100 kilometres of the DMZ, has 24 million inhabitants, many living in high-rise apartments. This guarantees high civilian casualties.

Level 4: Land war

Such escalation could initiate a land war.

Unlike in 1950-53, frontal tank-led assaults might count for less than special forces. North Korea's may number 180,000, the world's largest. Sent via undiscovered tunnels believed to traverse the DMZ, their potential to inflict damage and fear behind Southern lines (for instance using chemical and biological weapons) is considerable. Eventually, though, the allies' superior weaponry would see North Korea invaded, and the Kim regime eliminated.

Level 5: Limited Chinese intervention

At this point, indeed earlier, much would hinge on China's stance. Hopes in Seoul and Washington that Beijing might keep out if promised that no US bases will be built north of the DMZ are probably misplaced. As its reaction to THAAD deployment shows, China mistrusts US intentions and still values North Korea as a buffer state.

In any conflict, Chinese forces are thus likely at least to aid North Korea with materiel, while seeking to preserve the Kim regime or a more pliant alternative. On that goal there could, in theory, be common ground with Seoul, but the heat of battle will render cooperation difficult.

Level 6: Heavy Chinese intervention

Level 5, like Level 2, is unstable and therefore likely to escalate further. To ensure North Korea's survival, China would probably need to send its troops. A China-US confrontation is then possible.

Level 7: Nuclear escalation

If Kim Jong-un believes himself doomed, he has no incentive not to use his nuclear arsenal, with South Korea the nearest and surest target.

A recent study reckons that at least one nuclear-armed missile would probably get through South Korea's defences. One alone would kill an estimated 300,000 people at once, with many future deaths from radiation. In that case, the allies would feel justified in using nuclear weapons themselves.

Level 8: US-China nuclear war

The ultimate escalation would be if, observing the above and feeling that China itself was threatened by allied attacks, Beijing concluded that Washington was bent on bringing down China, too. China-US nuclear conflict would kill tens of millions in both countries, blighting the global economy for at least a generation and the planet long beyond.

It is hard to fathom how rational and responsible leaders in any nation would risk venturing even slightly down a path which could lead to such an outcome. However, it is one that at least some on both sides consider 'thinkable' and the potential for unplanned escalation is ever present.

Seeking stability

Establishing strategic stability after North Korea's acquisition of ICBMs requires Washington to recognise that its adversary can credibly target US forces, allies and population centres (see NORTH KOREA: Washington may eventually compromise - July 24, 2017).

Heightened rhetoric on both sides will generate diplomatic and public alarm, but is most likely a preliminary transition stage to mutual deterrence. However, Trump's inability to send credible signals increases the danger of miscalculation and will delay bilateral talks aimed at stability.