North Korea suffered an embarrassing spectacle over the weekend. Kim Jong Un, North Korea’s leader, ordered a missile launch to celebrate the 105th birthday of his grandfather, the country’s founding president. But the missile blew up almost immediately, ending a fairly impressive military parade through the streets of Pyongyang with the wrong kind of bang.

Still, the simple fact that North Korea continues to develop and test missiles — let alone nuclear weapons — means it will be one of the thorniest and most complex issues confronting President Donald Trump during his time in office. It also may be the most dangerous: A misstep could lead to open conflict with a nuclear-armed dictatorship run by one of the most mercurial leaders on earth.

If the standoff in North Korea becomes something much worse, Trump won't be able to say he wasn’t warned. As the Obama administration handed the White House keys over to the Trump team, the president told his successor that North Korea would be America’s top national security threat. And as predicted, things are headed south, with both Washington and Pyongyang now threatening “preemptive” strikes.

But when leaders like Trump and Obama sound alarm bells about the nebulous-sounding “North Korean threat,” what are they referring to?

First, and most critically, North Korea has nuclear weapons and ballistic missiles that when reliably combined could strike US allies in the region, like South Korea and Japan, where US troops are stationed. Thankfully, it still has some work to do before those nuclear-tipped missiles could reach American territory.

Second, North Korea has a vast array of artillery — that is, large guns usually used in land warfare — that could be used to attack South Korea. It also has a substantial chemical weapons stockpile, as well as elite special operations forces that could prove challenging for South Korea’s own forces to handle.

Finally, if North Korea does decide to use any of those weapons against its enemies, the aftereffects would pose their own significant, worldwide problems.

Let’s dig deeper.

North Korea’s nuclear weapons and ballistic missiles programs

This is the most obvious threat, but probably the most complicated.

Last year, Kim told other North Korean leaders that his country would conduct a nuclear strike if it was threatened by “invasive hostile forces with nuclear weapons.” It’s a pretty vague intimidation — nothing new when it comes to the North Korean leadership — but the implication is clear: If North Korea feels like its sovereignty or an important national interest is threatened, it will seriously consider using a nuclear weapon to respond.

To do that successfully, North Korea needs two things: a functioning nuclear weapon, and a way to deliver that weapon to a specific location. North Korea has both — but caveats apply.

There is currently no evidence that North Korea can place a nuclear warhead on an intercontinental ballistic missile (ICBM) and reliably hit any part of the US mainland or its territories. So when Sen. Dan Sullivan (R-AK), a member of the Senate Armed Services Committee, claims Kim “can press a button and hit Chicago,” he’s jumping the gun.

That said, North Korea has the potential to put a nuke on a medium-range missile that could reach South Korea and Japan — two allies that host US military installations. Simply put, if North Korea wanted to strike South Korea and Japan with a nuclear weapon, it could likely do so. Making matters worse, any nuclear strike on those countries would put American troops stationed there directly in harm’s way.

This is partially why the United States has decided to deploy the Terminal High Altitude Area Defense (THAAD) system in South Korea to defend against certain missile strikes and why America is conducting missile interception tests with Japan.

And the situation is likely to get worse. Jeffrey Lewis, director of the East Asia nonproliferation program at the Center for Nonproliferation Studies, told me in an interview that he thinks North Korea will have intermediate- to long-range missiles capable of carrying a nuke to American soil ready for launch in about five years. That will soon put Guam, and potentially Hawaii and other parts of the United States, within North Korea’s nuclear reach.

Let’s just stop for a second to let that sink in: Experts believe that in about five years, North Korea will be able to hit US territory with a nuclear weapon. And they think it can probably already hit Japan, South Korea, and US troops stationed there with a nuke right now.

That is the core of what we mean when we talk about “the North Korean threat.” It’s why this crisis feels so immediate, and why it seems to have been getting more and more frightening as time goes by.

It’s also because North Korea has dramatically ramped up the pace of its missile testing in recent years: In 2017 alone, the country conducted three successful missile tests — count ’em: one, two, three — and suffered two setbacks, including the one over the weekend. That’s on top of the five nuclear tests it’s conducted since October 2006, as the chart from the BBC below shows. The country currently claims to be “primed and ready” to carry out a sixth nuclear test any day now.

Despite stiff competition, Kim continues to vie for the title of most bombastic and overly confident world leader. He boasts his country can “wipe out Manhattan” if he so orders. He’s also threatened to reduce the United States “to ashes” if it strikes North Korea first. For now, these are laughably melodramatic statements, but if North Korea’s nuclear and missiles programs continue to improve at the same pace, those proclamations will quickly stop seeming like empty boasts.

Many important questions remain. For one, the size of North Korea’s nuclear arsenal is a mystery, although estimates put it somewhere between 10 and 16 weapons.

Second, it’s unclear if Pyongyang has what is known as a “second-strike capability” — that is, if North Korea were struck by a nuke, could it still retaliate with a powerful nuclear strike of its own? The jury is still out, but it is definitely trying to secure that capability. This matters a lot: If it has that ability, the stakes for any country thinking about attacking the North become exponentially higher, because they would then be susceptible to being hit by a North Korean nuke in response. In other words, it makes North Korea more dangerous and therefore gives them more leverage.

Finally, Kim claims he has a hydrogen bomb, a far more powerful type of nuclear weapon than the run-of-the-mill atomic bomb we know he already has. His assertion has not been proven — he more likely has a boosted atom bomb, which uses a radioactive form of hydrogen that makes it more powerful than a normal atom bomb but not nearly as powerful as a true hydrogen bomb. But if he does have a true hydrogen bomb, North Korea’s enemies have an even bigger threat on their hands than previously thought.

Artillery, chemical weapons, and special forces

While the nuclear and missile programs get all the attention, a seriously underappreciated threat comes from North Korea’s arsenal of conventional weapons, including the world’s largest artillery force. A third danger comes from the country’s elite special operations forces that could magnify the impact of a North Korean strike on South Korea.

South Korea’s capital city, Seoul, is a so-called “megacity” with a whopping 25.6 million residents living in the greater metropolitan area. It also happens to be within direct firing range of thousands of pieces of North Korean artillery already lined up along the border, also known as the demilitarized zone. Around 70 percent of North Korea’s ground forces are within 90 miles of the DMZ, presumably ready to move south at a moment’s notice.

Simulations of a large-scale artillery fight between the North and South produce pretty bleak results. One war game convened by the Atlantic back in 2005 predicted that a North Korean attack would kill 100,000 people in Seoul in the first few days alone. Others put the estimate even higher. A war game mentioned by the National Interest predicted Seoul could “be hit by over half-a-million shells in under an hour.” Those results don’t bode well for one of Washington’s closest allies, or for the tens of millions of people living in Seoul.

And that’s not all. A report from Stratfor, a private intelligence analysis firm, found that a large-scale North Korean artillery attack would likely mean that the northern half of Seoul would get hit the most. Depending on where North Korea placed some of its rocket launchers, southern portions of Seoul — including the Gangnam District of “Gangnam Style” fame — would also be within range.

The Stratfor report further notes than just “a single volley” of North Korean artillery could deliver “over 350 metric tons of explosives” into greater Seoul, “roughly the same amount of ordnance dropped by 11 B-52 bombers.”

As if that were not enough, North Korea has a robust chemical weapons program. South Korea’s Ministry of Defense estimates that its northern neighbor has between 2,500 and 5,000 metric tons of chemical weapons, including sarin and VX nerve agents. (Sarin is thought to be the chemical agent used in the Assad’s regime’s recent attack in Syria, which killed 72 people and left children gasping for breath as they choked on the poisonous gas.)

Should North Korea attack, it might use chemical weapons early on in South Korea’s urban areas to increase the death toll. At the same time, conventional munitions could rain down on the South. After that barrage, North Korea’s 200,000-strong special operations forces should have an easier time arriving via tunnels, mini-submarines, or Russian biplanes. Surely Pyongyang would find a way to employ its growing cyber capabilities, too, because why not?

Granted, North Korea is not expected to win a full-blown war with South Korea, should that come to pass. For one, America has the ability to stop a North Korean missile launch before it even happens with cyber capabilities.

But even if a launch did take place, the THAAD system being deployed in South Korea should be able to take it down. If that missed, Aegis ships in the Pacific could shoot the missile; and if that failed, Patriot batteries could also stop the flight. And if all that failed … well, you know. The bottom line is that there are lot of defenses in place designed to stop North Korean missiles, but nothing is perfect.

North Korea has far more troops than South Korea (1.19 million versus 655,000), but should a conventional fight break out, US and South Korean air power would help balance the scales. But, again, nothing is guaranteed.

Either way, North Korea could cause a lot of damage and harm a lot of countries — and people — as it goes down.

The aftermath of a conflict with North Korea “would be fundamentally disruptive” to the region — and the world

If there is a conflict where North Korea deploys many of its deadly weapons, what happens when the dust settles?

Robert Manning, a Koreas expert at the Atlantic Council, said in an interview that a North Korean attack on South Korea or any other of its neighbors “would be fundamentally disruptive” to the region and the world.

He’s not kidding. Marine Col. Jeff Vandaveer, who spent a year serving in Asia and was a former faculty member at the Marine Command and Staff College, has thought a lot about the potential regional and global effects of a war with North Korea. In an interview, he told me that such a conflict could lead to a big slump in the global economy, cause humanitarian suffering, and pit great powers against one another.

The economic consequences of Japan and/or South Korea, respectively the third and 11th biggest world economies, reeling from a big attack would impact the world’s financial future.

The humanitarian consequences would also be dire, Vandaveer said. Millions of hungry, displaced people would be trapped on a small peninsula during a brutal war. Meanwhile, tensions would rise as great powers like China, Russia, and the United States would likely be drawn further into the fray. That’s already happening, in a way, as Russian and Chinese ships tail America’s carrier strike group in the region. They both call for “restraint” in these tense times between America and North Korea.

Although the prospects of all-out war with North Korea are still pretty slim, Vandaveer’s depressing vision of the immediate aftereffects of a military exchange is the kind of scenario the Trump administration must plan for.

Trump seems to have gained a healthy appreciation of the seriousness and complexity of the North Korea challenge, calling it the “greatest immediate threat” to the United States. Initially, Trump thought China could use its economic and diplomatic influence over North Korea to quickly quell the threat. But after meeting with Chinese President Xi Jinping at Mar-a-Lago earlier this month, his perspective changed: “After listening for 10 minutes, I realized it’s not so easy,” Trump said, admitting his original solution was too simplistic.

The good news, in other words, is that Trump now has a more realistic sense of the enormity of the North Korea threat. The bad news is that it’s not clear that he has any real idea of what to do about it.

Alex Ward is an associate director of the Atlantic Council's Brent Scowcroft Center on International Security where he works on US foreign policy, national security strategy, and military affairs. You can follow him on Twitter @alexwardb.