North Korea warned this week that it was strengthening its “nuclear war deterrence.” Experts don’t know what that means, but they are worried. Given North Korean leader Kim Jong Un’s promise to develop a new strategic weapon if the United States did not build a new relationship with his country, concern is justified. Japan should be especially worried, not just because it has bitter, longstanding issues with North Korea, but because this country is on the top of Pyongyang’s target list.

Kim declared last year that U.S. President Donald Trump had until the end of 2019 to make a “bold decision” to end his country’s “hostile policy” toward North Korea. Trump made historical and unprecedented gestures to Kim but the two men proved unable, even after two summits and, according to Trump, “falling in love” as a result of Kim’s “beautiful letters,” to go beyond vague promises of denuclearization.

The new year came and went without any shift in U.S. policy — it continues to demand that North Korea give up its nuclear weapons and maintains sanctions to encourage it to do so — and security planners have been waiting for Kim’s threat to take shape. North Korea has maintained its self-imposed moratorium on nuclear and long-range missile tests, but it has conducted 18 tests of short-range missiles and rockets since May of last year; five rounds have occurred in 2020, and the country set a record for the most tests in a single month (nine) earlier this year.

In March, a statement from the Foreign Ministry for Negotiations with the U.S. declared that “we will go our own way. We want the U.S. not to bother us. If the U.S. bothers us, it will be hurt.” An unnamed official warned that his country has “become more zealous for our important planned projects aimed to repay the U.S. with actual horror and unrest for the sufferings it has inflicted upon our people.”

Last weekend, at a meeting of the ruling Workers’ Party’s Central Military Commission, Kim promised to implement “new policies for further increasing the nuclear war deterrence of the country and putting the strategic armed forces on a high alert operation,” reported the official Korean Central News Agency (KCNA). The CMC discussed “crucial measures for considerably increasing the firepower strike ability of the artillery pieces of the Korean People’s Army” along with ways to “reliably contain the persistent big or small military threats from the hostile forces.”

Experts believe that North Korea is developing a solid-fueled, mobile intercontinental ballistic missile that can deliver nuclear weapons anywhere in the world, specifically to threaten the U.S. homeland during a crisis. With enough fissile material to build over 50 weapons, an ever more modern — and threatening — nuclear capability is emerging.

It isn’t clear why the North wants that arsenal or what Pyongyang will do when it has it. The rhetoric above suggests two very different objectives: ensuring that North Korea isn’t threatened by the U.S. — deterrence — and righting past injustices — revenge. Nuclear experts also see an emerging North Korean strategy to use those weapons to compel other countries to act as it wishes; the ultimate expression of that thinking is to unify the Korean Peninsula by force under Pyongyang.

That sounds like a fantastic — as in “unbelievable” — ambition. But there is a logic to this approach. In a recent paper, Shane Smith, a nuclear expert at the U.S. National Defense University, points to North Korean exercises involving preemptive nuclear attacks on ports and airfields in neighboring countries as evidence of an emerging strategy to wage limited regional nuclear war while its long-range missiles keep the United States from intervening with its own nuclear weapons.

In short, Pyongyang is betting that a U.S. president won’t be willing to sacrifice Seattle for Seoul or New York City for Tokyo.

At first glance, that might seem plausible. The U.S. has been relatively restrained in the face of North Korean provocations, such as the sinking of the Cheonan, a Korean Navy ship, in 2010 or the shelling of Yeonpyeong Island several months later, which resulted in several deaths. In subsequent meetings with nuclear experts and officials from Japan and South Kore, that restraint was criticized as a failure of deterrence and likely to encourage more North Korean adventurism, a concern that has grown as Trump dismissed the short-range tests and derided the value of U.S. alliances.

The U.S. nuclear deterrent is not intended to prevent those attacks, however. A nuclear response to such a provocation is wildly disproportionate and to think that it would be used to respond to or prevent them is irresponsible. That doesn’t mean that the U.S. nuclear arsenal is useless or that the U.S. would be deterred by the prospect of retaliation.

The history of the Cold War shows that such thinking is wrong — the U.S. honored its alliance commitments despite a much larger and more credible Soviet nuclear capability — but Smith notes that “the types of weapons Pyongyang is building, the way it exercises and its public pronouncements about using them make it hard to dismiss that possibility out of hand.” The danger, then, is the prospect that North Korea takes its own rhetoric seriously and will misjudge the U.S. readiness to protect its allies and its interests.

While South Korea is likely to be the main target of a North Korean attack, Japan is one of the primary nuclear targets, if not the most likely one. A nuclear strike on Japan would disrupt the flow of personnel and material to the Korean Peninsula that is critical to dealing with a contingency. An attack would make plain to the Tokyo government the cost of allowing the U.S. to use facilities in the country to help defend South Korea. There is also probably a suspicion in Pyongyang that a substantial number of people in the region might secretly applaud, happy to see Tokyo pay again for past misdeeds.

For Japan, the U.S. and South Korea, the most important objective then is ensuring that the North Korean leadership harbors no illusions about the strength of U.S. alliances in Northeast Asia and Washington’s commitment to the defense of its allies. That means preparing — and demonstrating — a strong defense so that Pyongyang sees an adversary that is ready to fight if provoked. While that risks sending a message that the U.S. and South Korea (and Japan as it too prepares) are “hostile” to the North, it is intended to deter North Korea from picking a fight in the first place.

There are doubts about whether both U.S. alliances have been keeping pace with developments and are ready to fight in a nuclear environment. Looking at the U.S.-South Korea alliance, Smith sees little evidence of combined measures that would discourage Kim and his generals from thinking that they could deter the U.S. from intervening.

Smith provides a menu of ways to show U.S. and alliance resolve. The best way to discourage adventurism by the North, or any adversary for that matter, is for all three countries to be united in purpose and perspective and to demonstrate they will work together to address shared threats. (“Work together” includes sticks and carrots.)

Today, such coordination is problematic. There are tensions in every leg of the Japan-U.S.-South Korea triangle and while they are not yet sufficient to break those partnerships, they complicate and undermine needed preparations and allow adversaries to think that they have room to maneuver. Acting on that belief would be a tragic mistake, not just for Pyongyong, but for Japan, South Korea and the U.S. as well.

Brad Glosserman is deputy director of and visiting professor at the Center for Rule Making Strategies at Tama University as well as senior adviser (nonresident) at Pacific Forum. He is the author of "Peak Japan: The End of Great Ambitions."

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