In the aftermath of North Korea’s Sept 3 nuclear test, a Donald Trump Twitterstorm delivered its greatest disdain not to North Korea, but instead South Korea. Trump accused Seoul of being overly pacifist in the face of the North’s belligerence, as well as using a wide variety of measures to steal jobs from American workers. Later, piling on his own comments, Trump indicated that he was highly likely to soon withdraw completely from the United States’ free trade pact with South Korea.

Many found themselves head-scratching. The United States seems to be sliding towards a military confrontation with North Korea, and in any war scenario, coordination between the United States and South Korea would be key. As the New York Times editorial board summed it up,

“For Mr. Trump, the crisis lays bare how his trade agenda – the bedrock of his economic populist campaign in 2016 – is increasingly at odds with the security agenda he has pursued as president. It is largely a problem of Mr. Trump’s own making. Unlike several of his predecessors, who were able to press countries on trade issues while cooperating with them on security, Mr. Trump has explicitly linked the two…”

Unpacking all this – North Korea, South Korea, Trump and the relationship between trade and security – requires a few steps back.

American foreign policy since World War II has been based on a simple premise: the United States will create a global security structure for its allies, enabling them to access resources and markets the world over without the need to protect themselves, those resources or those markets. In exchange, those allies would allow the Americans to fight the Cold War their way. In essence the Americans bribed up an alliance via the Bretton Woods system to fight the Soviets, and in doing so not only attracted the allegiance of traditional cultural allies, but also countries with which the Americans had fought long, bitter wars – up to and including the former Axis and the U.S. own former colonial master. The end result was the strongest military alliance in human history, and also history’s longest and greatest period of peace and prosperity because nearly every imperial power of the past was on the same side (with the notable and obvious exception of the Soviet Union).

To put this in the Times‘ lexicon, trade and security were linked – with the Americans sacrificing their position on the former in order to gain deference on the latter.

The Cold War ended in 1989. The Soviet Union dissolved in 1992. And at the moment of truth when then-President George HW Bush stood poised to update America’s strategic policy, he was booted out of office in a federal election. His successor – Bill Clinton – had no time for foreign policy and so let the old system ride without a foe. The next U.S. President – George W Bush – pursued a monochromatic foreign policy completely focused on the Islamic world, and he too let the Cold War trade-for-security rubric continue, just without the trade-off. Then came Barack Obama who, in essence, didn’t have a foreign policy at all. Obama would on occasion go through the motions and say the right things about trade and allies, but actions were but rarely matched with words and the whole system atrophied. After 24 years of autopilot, the world barely resembles the bipolar alignment of 1945-1989. New power centers – think China – have emerged into what feels like a more multi-polar system.

Seoul, South Korea

This is the world the Times sees: trade and security are no longer linked. The United States negotiates on trade as an independent topic, while providing security for the global commons free-of-charge.

Everyone would do well to remember three facts:

First, throughout human history, there has never been a multipolar period in which widespread wars among constantly-shifting alliances were not the norm. If a post-American, multi-polar system really is where the world is headed, the future will be a dark, poor and war-torn place as various regional powers struggling for regional supremacy utterly overturn the global trade system that makes the world’s current safety, wealth and prosperity possible. For example, if the U.S. releases the security reins, Japan and China quickly fall into cutthroat competition over Middle Eastern oil. (Fun fact: there’s a full chapter on this “Tanker War” in The Absent Superpower.)

Second, all the powers that have arisen since 1989 are utterly dependent upon the security and trade systems the Americans created to fight the Cold War, and none of them are capable of taking up that burden from the United States. The U.S. Navy is more powerful than the combined navies of the rest of the world by a factor of ten (and that without nuclear weapons), and even if multiple powers could agree to pool their forces…whose interests would they look out for? It is hard to imagine the Chinese contributing to a force that facilitates French commercial penetration into Southeast Asia or the French navy providing the security environment required for Chinese commercial penetration into Belgium. If there is no American commitment to global order, there is no global order. That pushes every trans-national organization designed around a benevolent global security environment – that’s everything from the European Union to the Chinese Communist Party – over the brink.

Third, for the Americans, trade hasn’t been about economics – it’s been about security. Trade was the bribe to get all the world’s once-imperial powers to cooperate. Not only does an American withdrawal unleash heretofore quiescent powers as varied as Japan, the United Kingdom, and Iran to attempt to reshape their neighborhoods more to their liking, it further means that the Americans never really integrated their economy into the global whole like nearly everyone else did. And since the United States is by far the leastintegrated of the significant countries into the global trade system, it would be the one to suffer the least should that system collapse.

You might not care for Donald Trump very much, but if the United States is getting out of the global management business, you’ve got to admit that a rejiggering of the relationship between trade and security makes a lot of sense. (Whether the specifics of Trump’s preferred rejiggering make sense is, of course, an entirely different topic.)

And what about the raft of countries that did not even exist before 1945 because the various regional powers could easily subjugate them? What about places that in the intervening decades used this historic opportunity to transform themselves from backwaters to advanced economies? What happens to them when the global environment changes?

What happens to South Korea?

South Korea is a country roughly the size of Indiana with a mid-sized population and a gigantic role in global trade, currently ranking in the top ten in terms of total value of trade. Its markets span the world, with the majority not within a thousand miles. It sucks down vast volumes of raw materials – again, almost none of which are from East Asia – including over 2 million barrels of crude a day, almost all of which is sourced from the Persian Gulf. American economic sponsorship has transformed South Korea from being the world’s fifth-poorest country in 1953 to one of the richest. Remove the Americans from the world writ large, and South Korea would experience an economic crash at least twice as bad as the Great Depression.

Then there is South Korea’s military problem. The United States is South Korea’s security policy. U.S. troops not only face off against North Koreans opposite the demilitarized zone, American rapid reaction forces are stationed in Seoul, elsewhere in South Korea, Japan and throughout the Pacific to respond to any military situation the North might trigger. Remove the Americans, and the South Koreans lose air superiority, naval strike capability, ballistic missile reach, cruise missiles, missile defense and all those tough, zippy tanks. In a North-South war I firmly believe the South would emerge victorious – invasion routes through the DMZ are remarkably constrained and the South’s industrial plant and population are much larger than the North’s – but the damage to the south would be immense: North Korea has dug thousands of artillery emplacements into the hills on their side of the DMZ, most of which could target Seoul with withering fire. It isn’t something that anyone is looking forward to.

Finally, there is the overall American strategic angle:

Part and parcel of the Americans maintaining the Bretton Woods system is making the world safe and keeping the American market open for everyone. In the case of South Korea, that has come at immense cost.

As a mid-sized economy, South Korea could only develop with the direct physical and economic sponsorship of the United States. Resource-poor South Korea could have never obtained the raw materials and energy it needs without Bretton Woods. It would have never been independent without the U.S. military’s involvement in the Korean War and the decades since. It could have never grown without the American position in the Persian Gulf to ensure energy flows. It could have never built its infrastructure and industrial plant without American capital. It could have never exported its way to affluence without the American market. And there is meat to Trump’s trade accusations against South Korea: South Korea regularly uses everything from corporate welfare to state-sponsored intellectual property theft to advance corporate Korea’s interests.

The mismatch in the American mind between South Korea’s (lack of) commitment to American actions against North Korea, and the ongoing outlay of American blood and treasure for South Korea’s benefit has been an irritant in relations between Washington and Seoul since the Carter administration. The only thing that’s new about the recent criticism from the White House is that it is public. If the Americans really do back away from maintaining the global system, South Korea – as a country that cannot possibly field a navy capable of securing the markets and resources it needs – faces cataclysmic decline.

Yet while the South Koreans cannot do much about their economic exposure, they can do quite a bit about their military position. The land of Samsung, LG and Hyundai is one of the world’s most technologically advanced economies. Remove the Americans from the equation and the South will arm itself very rapidly. But tanks and planes and missiles all take time.

For a first-world country like South Korea with a lively civilian atomic power program, nukes are much easier. Delivering a ruggedized, miniaturized, thermonuclear weapon halfway around the world is hard stuff. But that’s not what South Korea would need to do. They’d just need a basic device they can lob a couple hundred kilometers. The South Koreans could probably build an explosive nuclear device in a matter of days, and mate it to a bare-bones delivery system shortly thereafter. The North Korean leadership – used to needling a Washington who views Pyongyang as a mere irritant rather than a terrified, angry sibling who knows just where to kick for the biggest effect – probably doesn’t not yet realize just how complicated their lives are about to become.

And keep in mind that North Korea is only South Korea’s danger-of-the-month. Before World War II, what is today’s South Korea tended to alternate between being an unwilling colony of Japan or China. Under most scenarios South Korea may be the runt of the neighborhood, but it will be a runt with a desperate population, a functional nuclear program and a couple million engineering doctorates used to making the impossible a functional reality. Poor, friendless, nuclear-armed, devilishly creative and testy – that is South Korea’s future.

The South Koreans won’t be alone.

Every country that was once either an imperial power or an imperial province is going to have to beef up its military simply to look after its own interests, and South Korea is hardly the only smallish country that lives in a dangerous neighborhood. A partial list of countries about to face drastically different security environments and starkly poorer economic futures while also boasting sufficient technical (and/or financial) skills to acquire a nuke include Sweden, Finland, Poland, Ukraine, Uzbekistan, Kazakhstan, Japan, Taiwan, Saudi Arabia and Turkey. All of which have pressing security concerns now, much less after the global security architecture collapses. For those of you into international relations, you may recall that some of the personalities that have topped some of those countries make Donald Trump seem calm, prudent and patient in comparison.

Each of these countries – indeed, nearly every country likely to go nuclear in the next couple of decades – sees a very specific security threat very close to home, and in no case is that threat the United States. One of the few topics on which I agree with today’s Twitterati is that a nuclear exchange is very likely a part of the not-so-distant future. But that doesn’t mean it’ll be part of America’s.