Something unusual – and perhaps unsettling in certain capitals – happened amidst the latest spasm of North Korean missile launches and nuclear tests: South Korea’s government leaked word that it has developed contingency plans to destroy the North Korean capital Pyongyang “as soon as the North shows any signs of using a nuclear weapon” against the South. In uncharacteristically blunt language, a South Korean military source warned, “The North’s capital city will be reduced to ashes and removed from the map.” Disclosure of the Republic of Korea’s (ROK) “Massive Punishment and Retaliation” plan underscores something the North Koreans, Chinese and even some U.S. officials seem to overlook: The ROK is not some appendage of Washington and is not obliged to ignore the North’s threats. Rather, the ROK is a sovereign nation that’s battle-ready.

ROK military sources say the South is prepared to launch preemptive strikes targeting “every Pyongyang district, particularly where the North Korean leadership is possibly hidden.”

Before we scold Seoul for employing such rhetoric, we should keep two things in mind.

First, the South’s rhetoric is tame compared to the North’s. Pyongyang’s endless war of words includes threats to turn South Korea into “a sea of fire,” declarations that the 1953 armistice is “completely nullified” and threats to conduct a “pre-emptive nuclear strike of justice” against the South.

Second, Pyongyang underlines its warlike words with warlike actions – and outright acts of war. In 2010, North Korea shelled South Korea’s Yeonpyeong Island (killing four South Koreans) and torpedoed an ROK warship in South Korean waters (killing 46 ROK sailors). In 2012, North Korea conducted two long-range missile tests under the guise of satellite launches. In 2013, Kim Jong Un detonated a nuclear bomb, proclaimed the 1953 armistice “dead” and threatened nuclear strikes against the United States and ROK. In 2015, we learned that North Korea had produced 20 nuclear warheads. And this year, Pyongyang has detonated two nuclear devices and conducted 21 missile tests.

North Korea’s missile launches and nuclear tests are increasing in frequency, the strength of its nuclear arsenal is increasing and the reach of its missiles is growing:

• This year marks the first time North Korea has conducted more than one nuclear test in a calendar year.

• The magnitude of North Korea’s nuclear tests, as measured by seismic activity, has grown with each detonation. According to weapons experts, the September test suggests“progress towards developing a miniaturized nuclear warhead.”

• U.S. officials conclude North Korea now has the ability to hit U.S. territory. As Adm. Bill Gortney, former NORTHCOM commander, concludes, “We assess that they have the capability to reach the homeland with a nuclear weapon from a rocket.”

• All told, since 2006, Pyongyang has conducted five nuclear tests; satellite launches (suggesting a threshold ICBM capability); multiple SCUD, short-range and medium-range missile tests; and test-firings of submarine-launched missiles.

All of this explains Seoul’s leaked defense plans and increasingly combative rhetoric. They are not empty words.

No longer a beleaguered nation reeling from war, South Korea is a vibrant liberal democracy, an economic dynamo, a contributor to international security and stability, and a formidable military power. Sixty-three years after starting from the very same place, the difference between North and South Korea is breathtaking: South Korea’s GDP is $1.85 trillion (14th globally), North Korea’s $40 billion (114th). South Korea’s per capita income is $36,500 (48th), North Korea’s $1,800 (210th). South Korea is thriving. North Korea is starving.

To be sure, Seoul counts on its partnership with Washington, but South Korea is no longer dependent on the United States for its preservation. Nor is it free-riding on the back of the U.S. military. Consider the division of labor: 600,000 ROK troops augmented by 28,500 U.S. troops. Or consider Seoul’s 2015 plan to increase defense spending by 7 percent per year between 2016 and 2020.

To its credit, the Obama administration has provided tangible evidence of America’s commitment to South Korea:

• Washington has made a habit of sending B-2s, B-1Bs, B-52s and F-22s on high-profile maneuvers over the peninsula to underscore America’s enduring support for its treaty ally on the southern side of the 38th Parallel.

• The United States is standing up a “combined division” with the ROK. “U.S. and Korean soldiers will literally operate as one unit,” explains Lt. Gen. Thomas Vandal, commanding general of the ROK-based 8th Army. “To the best of our knowledge, historically, we don’t know where it’s been done where you have brigades and staff headquarters fully integrated.”

• The U.S.-ROK command has developed a “counter-provocation plan” defining proportional responses to North Korean attacks. Announcing that such a plan exists sends a signal to Kim’s generals: While the U.S.-ROK objective is to prevent tactical incidents from triggering a strategic crisis, hostile acts will no longer go unanswered.

• This year’s annual U.S.-ROK exercises, which involved 17,000 American troops and 300,000 South Korean troops, were significantly larger than last year’s.

• U.S.-ROK naval exercises in September “marked the first time the allies have operated together in waters to the east of the peninsula near the North Korean border,” Stars and Stripes reports.

Next steps What can Washington and Seoul do to prevent the North from harming the South? Two steps are out of the question: withdrawal and preemption. Given the nature of the North Korean regime, either of those moves would invite the very thing no one wants: Korean War II.

Although there’s growing political support in America for turning inward and “letting other countries get along as best they can on their own,” withdrawing from the peninsula or even pulling back would leave the South exposed, tempt the North and destabilize the entire Asia-Pacific region (which depends on the steadiness of the U.S. alliance system).

If preemption was ever an option, it’s certainly off the table today, especially given the American public’s post-Iraq fatigue and North Korea’s nuclear capabilities. “Once an outlaw regime possesses nuclear weapons,” as historian Victor Davis Hanson observes, “it wins special consideration as the range of our own countermeasures diminishes.” Moreover, it pays to recall that President Bill Clinton ordered the Pentagon to develop plans for preemptive action against North Korean nuclear sites in 1994. The Air Force even conducted simulated counterproliferation strikes. But those plans never were executed, and understandably so. As the Congressional Research Service concluded, “The tactical success of a counterproliferation mission could be lost in the consequences of another war.”

The toll from Korean War I gives us pause: 38,000 Americans, 103,000 South Koreans, 316,000 North Koreans, 422,000 Chinese and some 2 million civilians killed during three years of conventional warfare. Today, we have the specter of a mushroom cloud hanging over the sequel. Moreover, Gen. Leon LaPorte, former commander of U.S. Forces-Korea, warned in 2005 that every third artillery round fired by North Korea would be a chemical weapon. And it’s worth noting that Korean War II would directly impact four of the largest economies on earth (South Korea, Japan, China and the United States) representing almost 50 percent of global GDP.

The fact that Korean War II would end the beastly Kim dynasty is of little comfort. Such a war would give new meaning to the term “Pyrrhic victory.”

All of this explains why the measure of success in Korea for U.S. presidents is simply getting through another day, another year, another term without another war. It’s a low bar. But given what Korean War II would look like, it’s a worthy goal.

If those are the steps to avoid, what steps can be taken?

Rebuild the arsenal The only thing that has prevented another war on the peninsula is America’s deterrent strength. Yet the U.S. defense budget has fallen from 4.6 percent of GDP in 2009 to 3.1 percent today – and if current projections hold, to just 2.7 percent of GDP in the coming decade. The last time America invested less than 3 percent on defense was 1940. This is the best way to invite the very worst of possibilities: what Churchill called “temptations to a trial of strength.”

U.S. policymakers should reverse this downward spiral, restore defense spending to the post-Cold War average of 4 percent of GDP and recognize that a well-equipped military is not a liability to cut but an asset to nurture. As President George Washington argued, “Timely disbursements to prepare for danger frequently prevent much greater disbursements to repel it.”

Pentagon officials convinced Seoul in July to allow deployment of a THAAD anti-missile system. This adds yet another layer of protection to the South, which already fields Patriot batteries, Aegis warships and long-range missile-tracking radars.

In June, South Korea joined the United States and Japan for the trio’s first-ever joint missile-defense exercises off the coast of Hawaii. Further integrating and networking these missile-defense systems will help shield Americans, Japanese and South Koreans from North Korean miscalculation or provocation.

Perhaps the next time a North Korean missile veers outside North Korean airspace, the allies should demonstrate their capabilities and seriousness – and knock it out of the sky. Tokyo appears poised to do just that.

Play the ace card Former State Department official Bennett Ramberg argues that in an era of declining defense budgets and rising instability on the peninsula, “reinstallation of nuclear weapons into South Korea ... would enhance deterrence” and “reassure the South Korean people.” Although Washington withdrew its nuclear deterrent in 1991, ROK officials have raised the prospect of redeploying U.S. nukes.

Of course, Seoul could always go nuclear on its own. “We can’t borrow an umbrella from a neighbor every time it rains,” says Won Yoo-cheol, a leading lawmaker in President Park Geun-hye’s ruling party. “It’s time for us to seriously consider an effective and realistic countermeasure for dealing with North Korea’s nuclear capability ... Only nuclear weapons could be an effective deterrence against nuclear weapons.”

Nearly two-thirds of South Koreans support developing a nuclear deterrent. Experts say it would take a matter of months for the South to go nuclear. If Washington wants to pressure Beijing to finally rein in its Frankenstein monster in Pyongyang, signaling Seoul that it’s OK to join the nuclear club would certainly get China’s attention. But like any gamble, there are risks to playing the nuclear card – especially on the Korean peninsula.