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The threat of nuclear war hangs over the Korean Peninsula.

This is nothing new. While the foam-flecked invective spilling out of North Korea is often taken with a generous pinch of salt south of the border, the cold reality is that Kim Jong Un is developing increasingly sophisticated nuclear weapons which threaten not only South Korea, but cities across the United States.

This week, new satellite images showed that North Korea is expanding its Yongbyon power plant site, the main factory for nuclear weapons material.

A nuclear-armed North Korea means the government in Seoul must grapple with a troubling thought experiement. If North Korea’s supreme leader decides to attack South Korea, the US would be obliged to intervene, according to the terms of a mutual defence treaty signed in the aftermath of the Korean War in 1953. But if Kim then threatens to launch a nuclear warhead towards the US mainland unless Washington withdraws from the conflict, what would the US do?

With the threat of Los Angeles reduced to a smouldering ruin, South Korean strategists worry that their superpower patron would back off.

This concern has fuelled popularity for the idea that South Korea should develop its own nuclear weapons. Yet in a landmark deal with the US in the last week, those ambitions appear to have been put on hold – for now at least.

A troubled peninsula

South Korea briefly flirted with the idea of developing nuclear weapons in the 1970s but ditched its covert weapons programme after the US got wind of it and threatened to withdraw all its troops from the country and kick South Korea out from under its nuclear umbrella.

In 1991, during the collapse of the Soviet Union – North Korea’s once-mighty backer – the US and South Korea agreed to withdraw all US nuclear weapons from the South’s shores. The idea was to persuade the North to also relinquish its nuclear programme, which by this time was well under way.

It didn’t work. Kim’s grandfather, and then father, carried on trying to develop the technology, while at the same time paying lip service to de-nuclearisation. North Korea admitted having developed nuclear weapons in 2005.

In 2019, Kim offered to shut down the Yongbyon power plant in return for the partial removal of international economic sanctions. President Trump refused, however, insisting on an “all or nothing” deal. Nuclear-capable weapons tests have ramped up since.

The nuclear option

In recent years, public opinion in South Korea has shifted substantially towards self-nuclearisation, rather than relying on the US nuclear arsenal – based outside South Korean territory – for protection.

A staggering 75% of the public are in favour of the idea, and President Yoon Suk Yeol even raised the possibility during a meeting of his defence chiefs, becoming the first South Korean president to openly propose arming the country with its own nuclear weapons. 

The Biden administration thought it best to do a deal. To avoid nuclear proliferation on the Peninsula, while also guaranteeing South Korea’s safety, presidents Biden and Yoon signed the “Washington Declaration” last week. The US agreed to deploy nuclear-armed submarines to South Korea and involve Seoul in its nuclear planning to counter nuclear threats from the North.

In return, South Korea agreed to not develop its own nuclear weapons. Yoon reaffirmed South Korea’s commitment to the Nuclear Nonproliferation Treaty, a legal restraint to Seoul developing its own nuclear weapons stockpile.

No guarnatees

Washington’s diplomatic manoeuvring in the past week has shifted the delicate dynamics of the Peninsula’s nuclear power struggle. 

Other factors could also change the equation, however. China, for instance, could possess more than 1,000 nuclear warheads by 2030, according to the Pentagon. And South Korea’s own nuclear ambitions will only be contained as long as the US maintains a credible nuclear deterrent in the Pacific. 

The situation is evolving, but the nuclear threat isn’t going away.

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