North Korea (officially called the Democratic People’s Republic of Korea) is isolated, impoverished, and a proclaimed enemy of its southern neighbor, South Korea—an important U.S. ally.
U.S. military involvement in the Korean peninsula has its roots in the Korean War of the early 1950s during the early stages of the Cold War, in which the United States supported forces in the southern part of the peninsula against communist forces in the north, who were aided militarily by China and the Soviet Union. Today, the United States is committed to defending South Korea (also known as the Republic of Korea) under the terms of the Mutual Defense Treaty between the United States and the Republic of Korea. The United States has nearly 29,000 troops deployed in the Korean peninsula for that purpose. In addition to U.S. troops, many of South Korea’s 630,000 troops and North Korea’s 1.2 million troops are stationed near the Demilitarized Zone (DMZ), making it one of the most heavily armed borders in the world.
In violation of UN Security Council resolutions, North Korea continues overt nuclear enrichment and long-range missile development efforts. Although the scale of North Korea’s uranium enrichment program remains uncertain, U.S. intelligence agencies estimate that it has enough plutonium to produce at least six nuclear weapons, and possibly up to sixty.
In September 2017, North Korea conducted its sixth nuclear weapons test, its most powerful test to date. As with previous tests in 2016, it again claimed to have developed a hydrogen, or thermonuclear, bomb, which would represent further advancements in the nuclear program and the ability to build more powerful, higher-yield nuclear weapons. Since February 2017, North Korea has conducted sixteen missile tests with a total of twenty-three missiles, including a missile that it says can carry a nuclear warhead. Four of the missiles failed. In early July 2017, the country conducted its first successful test of an intercontinental ballistic missile (ICBM). Three weeks later, it tested another ICBM that experts believe could reach the continental United States. In August 2017, U.S. intelligence agencies determined that North Korea can miniaturize its nuclear weapons to fit inside a missile, which North Korea had already claimed it could do in March 2016. In November 2017, North Korea conducted the first test of a previously unseen missile, reportedly its largest ICBM yet, the Hwasong-15. However, North Korea has not yet demonstrated that its nuclear warheads can withstand reentry into Earth’s atmosphere.
In response to the increasing frequency of missile tests, the United States has deployed an anti-missile system in South Korea. The Terminal High Altitude Area Defense (THAAD) system is located in the Seongju region of South Korea, one hundred and fifty-five miles from the northern border.
The United States, South Korea, and Japan have each passed their own unilateral sanctions against North Korea, targeting companies involved in North Korean missile and nuclear weapons development, high-ranking individuals, and sources of income for the North Korean government. Following the second ICBM, in August 2017 the UN Security Council unanimously passed its harshest sanctions yet on North Korea, targeting some of the most important sources of revenue for the regime including North Korean exports and banning the country from sending more workers abroad. In November 2017, the United States placed North Korea back on a list of state sponsors of terrorism, a move that enables additional sanctions to be placed on the regime.
Kim Jong-un’s willingness to provoke the West with aggressive behavior has exacerbated the threat from North Korea’s weapons proliferation. These incitements have included firing missiles over northern Japanese islands, firing rockets across the South Korean border in August 2015, and a cyberattack on U.S.-based Sony Pictures in December 2014.
Kim has also undertaken efforts to consolidate his power by purging high-ranking officials, including his own family members. In February 2017, Kim's half-brother was killed using a banned nerve agent in an airport in Malaysia. North Korea denies responsibility for the attack. There are reportedly between 80,000 and 120,000 political prisoners detained in North Korea. This consolidation of power may suggest that Kim, fearing fewer internal challenges to his control, is increasingly unconstrained domestically in making policy decisions.
North Korea is a nuclear power with a complex relationship with China, and preventing both an interstate Korean war and a North Korean internal collapse are critical U.S. national security interests. Along with continued weapons and missile tests, small-scale military and cyber provocations by North Korea pose significant risks as each incident carries with it the potential for further and potentially uncontrollable escalation. Outright threats from North Korean Supreme Leader Kim Jong-un are also cause for concern, as he claims that North Korean weapons can now reach U.S. territories and even the U.S. mainland.
In early 2018, North and South Korea began a diplomatic rapprochement, and North Korean officials attended the Opening Ceremony of the Winter Olympics in Pyeongchang, South Korea. On April 27, a week after announcing that North Korea would freeze weapons and missile testing, North Korean Supreme Leader Kim Jong-un stepped across the border into South Korea for a summit with South Korean President Moon Jae-in. The leaders signed a joint statement pledging to work toward denuclearization of the Korean peninsula and an official end to war between the two countries.
There has also been a marked change in U.S. policy toward North Korea. In June 2018, President Donald J. Trump and Kim Jong-un met in Singapore and released a joint statement about denuclearization. The leaders met again in Vietnam in late February 2019, but ended the summit early without making a deal or announcement.