When Russian President Vladimir Putin traveled to Pyongyang in June 2024, his first visit to North Korea in nearly a quarter century, the optics were striking. Russian flags and portraits of Putin adorned the capital, where he was treated to an elaborate welcome ceremony with a military honor guard and groups of balloon-toting children. But this was to be expected; such pageantry is a hallmark of North Korean politics. Less anticipated was the substance of Putin’s subsequent meeting with North Korean leader Kim Jong Un. The Treaty on Comprehensive Strategic Partnership the two men signed that day formalized a relationship that had been quietly taking shape since Russia’s full-scale invasion of Ukraine in 2022: a military alliance between two nuclear-armed pariah states. By October 2024, around 11,000 North Korean troops had been deployed to Russia, primarily in the Kursk region along Ukraine’s northeastern border, to support Russian combat operations. By late April 2025, South Korean intelligence assessments put Pyongyang’s troop presence at around 15,000, and at least half that number remain deployed.

The partnership has made a significant difference in Russia’s war effort. North Korea’s conventional military is often written off as small and underdeveloped, but the country has become a key supplier of artillery ammunition, select missiles, and manpower to Russia. In February 2025, Ukraine’s military intelligence chief publicly claimed that North Korea was providing about half the ammunition Russia was using at the front. Based on Ukrainian military intelligence estimates from November 2025, North Korea has supplied Russian forces with around 6.5 million artillery rounds since 2023 and with sophisticated long-range self-propelled artillery systems and multiple launch rocket systems since late 2024.

The partnership is making the Korean Peninsula a more dangerous place, too. Not only has North Korea gained military capabilities from Russia and experience from fighting in its war, but deepening economic and diplomatic ties between the two countries have relieved some of the pressure that for decades has kept North Korea subordinate to China. Now, with more confidence in its conventional military and in a position to play two great-power patrons off each other, North Korea faces fewer constraints than ever before. And should Pyongyang choose aggression against its southern neighbor, the resulting war would likely not be limited to a fight between North Korea and a U.S.-backed South Korea but draw in Russia and China, as well.

U.S. policymakers have been hoping to offload some of the responsibility for maintaining peace on the Korean Peninsula to Seoul. But Washington has missed the fact that this task has fundamentally changed. Deterring Pyongyang now means deterring Beijing and Moscow, too, and South Korea, as capable as it is, cannot do this alone. For Washington to step back at this perilous moment would raise the risk of war even further and push the United States into the very situation it should want to avoid: embroilment in a conflict with North Korea, China, and Russia—nuclear powers all.

The Korean Peninsula has been one of the world’s most dangerous flash points since North Korea, with the support of communist China and the Soviet Union, invaded South Korea in 1950. The United States led a 16-country United Nations force to defend South Korea; China intervened a few months later on behalf of North Korea. The fighting lasted three years, stopping only after two years of tortuous, on-and-off negotiations. The resulting armistice created the demilitarized zone (DMZ), which now serves as the border between North and South Korea. Because the two countries never signed a peace treaty, they are technically still at war. The possibility of a second North Korean invasion or regime collapse in Pyongyang has driven U.S. and South Korean military planning ever since.

Over the past seven decades, direct clashes, provocations, and close calls have repeatedly tested the armistice. In 1968, North Korea sent a 31-man commando unit to Seoul in an audacious attempt to assassinate South Korean President Park Chung-hee, and days later, its navy seized the USS Pueblo, an American intelligence vessel. In the 1970s, South Korean soldiers discovered that secret tunnels had been dug under the DMZ, and North Korean soldiers killed two American officers in the zone’s Joint Security Area, an incident that nearly triggered open conflict. Confrontations in the Yellow Sea led to deadly clashes in 1999, in 2002, and, most dramatically, in 2010, when North Korea torpedoed the South Korean corvette Cheonan, killing 46 sailors, and then shelled Yeonpyeong Island, wounding and killing both soldiers and civilians.

The danger on the peninsula gained a nuclear dimension in the 1990s, when North Korea announced its plan to withdraw from the Nuclear Nonproliferation Treaty. Negotiations with the United States delayed Pyongyang’s formal withdrawal until 2003, but afterward North Korea quickly advanced its weapons development, conducting six nuclear tests between 2006 and 2017. Pyongyang’s intercontinental ballistic missile test in 2017, meanwhile, demonstrated for the first time a potential capability to reach the continental United States—a threat it has since reinforced with additional tests and technological development. After a brief diplomatic opening in 2018, when Kim joined meetings with both South Korean President Moon Jae-in and U.S. President Donald Trump, ended with no lasting agreements, North Korea accelerated its missile testing. It has continued to expand its nuclear arsenal in the years since. As Kim declared in a speech in March, the country now possesses “the power to pose a threat if necessary.”

North Korea faces fewer constraints than ever before.

Today, the lessons North Korea is learning in Ukraine are also strengthening its capacity to launch limited attacks, which increases the likelihood that a clash could escalate to general war. To be sure, a hypothetical conflict on the Korean Peninsula would not look quite the same as the war in Ukraine, so Pyongyang’s on-the-ground experience would not give it a decisive edge. North Korea would face a more formidable opponent than the one Russia faced when it first invaded Ukraine: the South Korean military, with half a million troops and modern high-tech equipment, has been planning, exercising, and stockpiling in preparation for a North Korean attack for more than 70 years, and it would likely be joined by the United States in combat, given that around 28,500 U.S. troops are stationed in South Korea. Yet North Korea would have advantages, too. It could put Seoul at risk without advancing first; the city and its more than ten million inhabitants are only about 30 miles from the DMZ, well within range of North Korea’s nearly 6,000 artillery systems. And at less than 160 miles, the DMZ line running across the Korean Peninsula would be far shorter than the 750-mile frontline today in Ukraine—favoring North Korea at the outset by allowing it to concentrate its forces and deliver a powerful opening salvo.

After a war got underway, North Korea, like Russia, would rely on massed artillery to suppress South Korean and U.S. defenses, disrupt command and control, and strike major military targets around Seoul. It would be unlikely to gain air superiority, so its ground forces would have to adopt dispersal and concealment methods to avoid air attacks. And it would likely need to use its short-range missiles in the same way Russia is using these North Korean weapons today, to strike logistics nodes, command posts, air defense systems, and infrastructure. The thousands of North Korean troops sent to Russia—the first large-scale deployment of North Korean forces to a foreign theater since the Cold War—are learning how to do all of this. This cohort has suffered significant casualties; as of February, South Korean intelligence estimated that about 6,000 soldiers, more than a........

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