North Korean leader Kim Jong Un walks around a intercontinental ballistic missile in North Korea, March 24.

Photo: /Associated Press

Rocket Man is on another blasting spree. Last week Pyongyang tested a “monster” intercontinental ballistic missile, reportedly designed to strike any spot in the U.S. and overwhelm American missile defenses with multiple warheads. Since the beginning of the year North Korea has conducted more than a dozen launches—including cruise, rail-based, hypersonic and intermediate-range ballistic missiles—as well as an unsuccessful long-range missile test earlier this month. But why now? What does Kim Jong Un want from his sudden fireworks display?

The explanations from Washington and Asian capitals for these latest launches sometimes sound like the naive foreign-policy punditry from the 1990s, at the very start of Pyongyang’s methodical march to nuclear status. We hear that the Kim regime is trying to get our attention, for example, or that it is shoring up its domestic legitimacy.

Have we really learned so little from a generation of confrontation with this revisionist state? By now it should be clear to observers that Pyongyang fires off new weapons because their development is vital to its fundamental strategic goal of unifying the Korean Peninsula under Kim rule.

To achieve unconditional unification on its own terms, North Korea would first have to break the U.S.-South Korean military alliance. Pyongyang hopes to do that through a nuclear showdown with America. We don’t need to guess about this. Immediately after the latest ICBM launch, one North Korean media outlet explained Mr. Kim’s reasoning for building these new armaments: “the long-term demand of our revolution,” the North Korean term for conquest of the South, presupposes “the inevitability of the longstanding confrontation with the U.S. imperialists.” The logic is simple: No weapons testing, no unification.

This is why regular and recurrent missile launches and nuclear detonations are an essential and entirely predictable feature of North Korea’s behavior. New weaponry has to be tested before the North’s scientists and generals can be certain that it works. Pyongyang is totally committed to strategic modernization, for which Mr. Kim laid out a program in detail at the Party Congress early last year. Advancing that agenda will require continual performance checks on the new equipment, just as past progress in nuclear and missile capabilities necessitated North Korea’s previous experiments.

But why the current flurry of launches? The likely answer is that this is simply Pyongyang’s first opportunity to conduct them. Though Pyongyang has proved adept at keeping outsiders in the dark about its weapons programs, the record suggests North Korea tests prototypes essentially as soon as it can.

The regime seems unwilling (perhaps doctrinally incapable) of waiting until later to test its munitions when it can launch them now—hoping to rush them to mass production as soon as possible.

Planned tests are of course sometimes scheduled for propagandistic considerations—July 4 and North Korean national holidays being especially favored dates for launches and explosions. But the North generally seems to test its new equipment as soon as it is deemed ready, which sometimes turns out to be before it actually is, as this month’s launchpad failure of a long-range missile attests.

Yet for all its haste, Pyongyang also takes curiously long breaks between launches. It’s been more than four years since the North last tested an intercontinental ballistic missile.

Outsiders know precious little about the workings of the overall North Korean economy and even less about its defense sector, but it’s a fair guess that protracted hiatuses between weapons tests are often the result of resource constraints. North Korea’s economy is tiny, inefficient and undependable, while missile and nuclear programs are exacting and extremely expensive (and all the more costly for technologically backward societies). Furthermore, the North Korean economy is painfully prone to unexpected dislocations and severe slumps.

The most recent tests signal that the North Korean economy is finally recovering after Mr. Kim’s draconian Covid lockdowns all but incapacitated it. Economic constraints may also be a reason Pyongyang’s weapons testing dropped off after the United Nations Security Council’s 2017 spate of comprehensive economic sanctions. And they could help explain why the tempo of missile and nuke tests under Kim Jong Il (a notoriously miserable economic manager, even by North Korean standards) was so much slower than under his son Kim Jong Un before those 2017 sanctions. Declaring a self-imposed moratorium—as the North did in 2018—sounds so much better than saying you are unable to scrape together the cash.

President Biden caught a break by entering office while North Korea was suffering from acute, if self-inflicted, economic woes. The recent spate of missile tests suggests North Korea’s weapons programs are back in the black. Further menacing tests may lie in store—we shouldn’t rule out nuclear ones. And the return to testing means we should also expect a resumption of North Korea’s brand of nuclear diplomacy.

Rather than trying to appease Mr. Kim, the Biden administration and the rest of the international community would be well served in identifying, and squelching, the new resource flows funding the North Korean war machine. Pyongyang has launched a lucrative new career in cybercrime. The Kim regime has also benefited from Russian and Chinese sanction-busting. There could well be other illicit revenues worth pursuing; the U.S. intelligence community should find out.

Thirty years of fruitless attempts at diplomatic engagement with the North have demonstrated that outsiders can’t alter the regime’s determination to become a nuclear power. But forceful international economic penalties, tirelessly and creatively applied, can throw sand in the gears of the North’s military programs. We should address this task with the seriousness it deserves. If we don’t try to stop North Korea from becoming a greater threat, we will enter a world in which Pyongyang can credibly threaten the American homeland with nuclear missiles.

Mr. Eberstadt holds a chair at the American Enterprise Institute and is a senior adviser to the National Bureau of Asian Research.