We take a look at the significance of the declaration, and whether it could make North Korea change its direction.

If North Korea uses its nuclear weapons against the United States or its ally South Korea, it would be “the end” of Kim Jong Un’s regime, Seoul and Washington announced this week.

The stern threat comes as South Korea’s President Yoon Suk-yeol is on a six-day state visit to the US, where he and his counterpart Joe Biden discussed ramping up the US security shield for South Korea in the face of the nuclear-armed North’s increased missile tests.

But how significant is the tough-sounding statement? Here is what we know.

What is the Washington Declaration, and what does it do?

• It is a set of new steps that boost US-South Korean military cooperation and information sharing.
• The declaration includes the creation of a “Nuclear Consultative Group” to give South Korea additional insight into US planning for major contingencies and “a voice in those deliberations”.
• It also includes the regular deployment of a US nuclear-armed ballistic missile submarine (SSBN) to South Korea – something that has not happened since the 1980s – and other measures, including more information sharing in the event of a North Korean attack.
• But there are no plans to station US nuclear weapons in South Korea, and some analysts doubt the declaration’s practical value.

Is it significant?

• The state visit undoubtedly “represents a new high-water mark for US-South Korea relations, with the breadth and depth of security, economic, and cultural cooperation on full display”, Leif-Eric Easley, a professor at Ewha University in Seoul, told AFP.
• Yoon has been trying to reassure the South’s increasingly nervous public about the US commitment to so-called “extended deterrence”, where US assets – including nuclear weapons – serve to prevent attacks on allies.
• A major problem is not the agreement but the US political landscape, which means the agreement could be worthless after the 2024 presidential election there, Karl Friedhoff at the Chicago Council on Global Affairs told AFP.
• The potential return to power of former US President Donald Trump is likely to trigger “very serious discussions” in Seoul, he said.
• For the US-South Korea relationship, “the biggest challenge is something that the alliance doesn’t really have any control over: US domestic politics“, Friedhoff said.

Why is South Korea concerned?

• The US’s “extended deterrence” protection for South Korea rests on a simple assumption: that the US would retaliate if North Korea uses nuclear weapons against South Korea.
• For years after Pyongyang first tested a nuclear bomb in 2006, this was a believable threat. North Korea had relatively few bombs and limited ability to send them far beyond its own borders.

• But North Korea’s arsenal has grown, and it now has intercontinental ballistic missiles (ICBMs) that can reach US cities, making the cost of defending South Korea potentially far higher.
• Sceptical that the US would risk its own cities to defend its ally, a majority of South Koreans now believe the country should develop its own nuclear weapons, recent surveys show.
• “A nuclear attack by North Korea against the United States or its allies and partners is unacceptable, and will result in the end of whatever regime were to take such an action,” Biden said standing alongside Yoon at the White House.

Will Seoul get nuclear weapons?

• Under the agreement, South Korea reaffirmed its commitment to “its obligations under the Nuclear Non-Proliferation Treaty as the cornerstone of the global non-proliferation regime”.
• “One thing was clear: there was an implied agreement that Seoul would not go nuclear,” said Soo Kim, policy practice area lead at LMI Consulting and a former CIA analyst, told AFP. “Seoul’s nuclear ambitions have been capped.”
• Gi-Wook Shin, a Korea expert and sociology professor at Stanford University, told AFP that the declaration was “a step forward”.
• “I don’t think this will be enough to appease a South Korean public that has increasingly demanded that Seoul develop nuclear weapons of its own,” Shin said.

What will North Korea do?

• Closer cooperation between its self-declared arch enemies, Washington and Seoul, is bound to concern Kim Jong Un’s regime and there could be more missile launches to demonstrate this, experts say.
• In public, “North Korea will downplay the message of reassurance by the US regarding nuclear deterrence”, Chun In-bum, a retired South Korean army general, told AFP.
• But behind closed doors, “they will get the message: if they use nuclear weapons it will be the end of the regime”, he said.
• According to experts, it’s still unlikely that North Korea will change its position.
• “It is unlikely that North Korea will give up its nuclear weapons by giving in to these threats,” Yang Moo-jin, president of the University of North Korean Studies in Seoul, told AFP.