After a year in which he tested a hydrogen bomb and an ICBM, threatened to destroy the United States, and called President Trump “a dotard,” Kim Jong Un, at the gracious invitation of the president of South Korea, will be sending a skating team to the “Peace Olympics.

An impressive year for Little Rocket Man.

Thus the most serious nuclear crisis since Nikita Khrushchev put missiles in Cuba appears to have abated. Welcome news, even if the confrontation with Pyongyang has probably only been postponed.

Still, we have been given an opportunity to reassess the 65-year-old Cold War treaty that obligates us to go to war if the North attacks Seoul, and drove us to the brink of war today.

2017 demonstrated that we need a reassessment. For the potential cost of carrying out our commitment is rising exponentially.

Two decades ago, a war on the Korean Peninsula, given the massed Northern artillery on the DMZ, meant thousands of U.S. dead.

Today, with Pyongyang’s growing arsenal of nuclear weapons, American cities could face Hiroshima-sized strikes, if war breaks out.

What vital U.S. interest is there on the Korean Peninsula that justifies accepting in perpetuity such a risk to our homeland?

We are told that Kim’s diplomacy is designed to split South Korea off from the Americans. And this is undeniably true.

For South Korean President Moon Jae-in is first and foremost responsible for his own people, half of whom are in artillery range of the DMZ. In any new Korean war, his country would suffer most.

And while he surely welcomes the U.S. commitment to fight the North on his country’s behalf as an insurance policy, Moon does not want a second Korean war, and he does not want President Trump making the decision as to whether there shall be one.

Understandably so. He is looking out for South Korea first.

Yet Moon rightly credits Trump with bringing the North Koreans to the table: “I give President Trump huge credit for bringing about the inter-Korean talks, and I’d like to thank him for that.”

But again, what are the U.S. interests there that we should be willing to put at risk of nuclear attack tens of thousands of U.S. troops in Korea and our bases in Asia, and even our great cities, in a war that would otherwise be confined to the Korean Peninsula?

China shares a border with the North, but is not treaty-bound to fight on the North’s behalf. Russia, too, has a border with North Korea, and, with China, was indispensable to saving the North in the 1950-53 war. But Russia is not committed by any treaty to fight for the North.

Why, then, are Americans obligated to be among the first to die in a second Korean War? Why is the defense of the South, with 40 times the economy and twice the population of the North, our eternal duty?

Kim’s drive for a nuclear deterrent is propelled by both fear and calculation. The fear is that the Americans who detest him will do to him and his regime and country what they did to Saddam Hussein.

The calculation is that what Americans fear most, and the one thing that deters them, is nuclear weapons. Once Soviet Russia and Communist China acquired nukes, the Americans never attacked them.

If he can put nuclear weapons on U.S. troops in Korea, U.S. bases in Japan, and U.S. cities, Kim reasons, the Americans will not launch a war on him. Have not recent events proven him right?

Iran has no nuclear weapons and some Americans clamor daily for “regime change” in Tehran. But because Kim has nukes, the Americans appear more anxious to talk. His policy is succeeding.

What he is saying with his nuclear arsenal is: As you Americans have put my regime and country at risk of annihilation, I am going to put your cities at risk. If we go down in your nuclear “fire and fury,” so, too, will millions of Americans.

The whole world is watching how this plays out.

For the American Imperium, our system of alliances, is held together by a credible commitment: If you attack any of our scores of allies, you are at war with the United States.

From the Baltic to the Black Sea to the Persian Gulf, from the South China Sea to Korea and Japan today, the costs and the risks of maintaining the imperium are growing.

With all these promissory notes out there—guarantees to go to war for other nations—one is inevitably going to be called.

And this generation of Americans, unaware of what their grandfathers obligated them to do, will demand to know, as they did in Iraq and Afghanistan: What are we over doing there, on the other side of the world?

“America First” is more than a slogan.

Patrick J. Buchanan’s latest book is Nixon’s White House Wars: The Battles That Made and Broke a President and Divided America Forever.