Engagement and the “sunshine policy”

At the turn of the 21st century, many Koreans believed that the time might be near when the peninsula would be reunified. Kim Dae-Jung’s sunshine policy led to a summit with the North Korean leader, and some families were permitted to travel across the border for reunions. In 2003 construction began on a joint North-South industrial complex and duty-free trade facility at Kaesŏng, North Korea, that had been planned during a period of warming relations in the late 1990s. Within a few years, several dozen South Korean companies had facilities there, among them textile, chemical, machinery, and electronics factories. The businesses employed both North and South Koreans, and tourist groups were permitted to visit the complex from South Korea. In addition, at the 2000 Summer Olympic Games in Sydney and at several Olympics and Asian Games thereafter, North and South Korean athletes marched under a single flag (one showing a silhouette of the peninsula) during the opening and closing ceremonies, though they competed as separate teams.

Nevertheless, relations subsequently soured as North Korea admitted it had continued developing nuclear weapons; in 2005 the North revealed that it possessed such weapons, and in October 2006 it tested its first nuclear device. Dialogue between the two sides continued, however, resulting in two significant events in 2007: in May trains from both the North and the South crossed the demilitarized zone to the other side, the first such travel since the Korean War; and in October Roh Moo-Hyun met Kim Jong Il in Pyongyang for a second summit.

Increased tensions with the North

The December 2007 election of Lee Myung-Bak as South Korean president began another period of deterioration in inter-Korean relations as Lee took a harder line with Pyongyang. In 2008 North Korea announced that it planned to close the land border and all nonmilitary telephone links with South Korea. North Korean officials followed up on those pronouncements in January 2009 when they stated that all military and political agreements with South Korea would be nullified; in May of that year the North further announced that all business contracts pertaining to the joint North-South Kaesŏng Industrial Complex would be canceled.

In March 2010 a South Korean warship, the Cheonan, exploded and sank in the waters of the Yellow Sea near Baengnyeong Island, close to the maritime border with North Korea. The incident’s proximity to the border prompted the South Korean military to be placed on alert. A large-scale rescue operation saved 58 of the 104 sailors aboard the ship. Two months later an international team of investigators determined that the explosion had been caused by a torpedo fired from a North Korean submarine. The news increased tensions between the two countries even further. Although the North Korean government denied responsibility for the attack, South Korea suspended trade relations with its northern neighbor and declared its intention to resume propaganda broadcasts along the border.

Although a cross-border reunion for hundreds of North and South Korean family members was held in late October 2010, there was no resolution to the Cheonan incident, and tensions continued to be high. In late November, as South Korea was conducting a military exercise off the country’s northwestern coast, the North Korean military bombarded the South Korean border island of Yeonpyeong—the scene of offshore naval skirmishes in 1999 and 2002—with artillery shells. The shells hit a military base and civilian homes, and there were several casualties. South Korean forces returned fire and raised the level of military preparedness on the island. The incident was considered one of the most serious episodes of hostility between North and South in years.

Kim Jong-Un and the maturation of the North Korean nuclear program

The death of Kim Jong Il in December 2011 ushered in a new era of uncertainty. His youngest son, Kim Jong-Un, succeeded him as North Korea’s supreme leader, and the North’s nuclear program accelerated. Despite agreeing to suspend missile and nuclear weapon development in 2012 in exchange for food aid, the country conducted its third nuclear test in February 2013. The North claimed that it had conducted a hydrogen bomb test in January 2016, but observers noted that the seismic readings associated with the explosion were consistent with a low-yield fission device. In response to the North’s continued pursuit of nuclear weapons and ballistic missile technology, in July 2016 South Korea and the U.S. announced the deployment of a theater missile defense system, Terminal High Altitude Area Defense (THAAD), in Seongju, South Korea.

The election of Moon Jae-In as president in May 2017 seemed to signal a dramatic shift in policy. Moon’s predecessor, Park Geun-Hye, had adhered to an adversarial approach typical of conservative South Korean politicians. Moon, in a move that echoed Kim Dae-Jung’s sunshine policy, advocated engagement with the North and opposed such defensive measures as THAAD. When the North ratcheted up its aggressive rhetoric and test launched an ICBM in July 2017, however, Moon reversed himself and announced that his government would work with the U.S. to deploy the complete THAAD system.

As tensions on the peninsula reached their highest point in years, with Kim Jong-Un and U.S. Pres. Donald Trump trading threats and insults, the 2018 Winter Olympic Games in Pyeongchang, South Korea, provided an unlikely avenue for rapprochement. The North and South Korean contingents arrived together at the opening ceremonies, marching under a single banner that depicted a united Korea on a field of white. Moon met with Kim’s sister, Kim Yo-Jong, and a series of high-level contacts were initiated between the North and the South. Those preliminary engagements paved the way for a summit in April 2018 that saw the leaders of North and South Korea meet for direct talks for the first time in over a decade. At the conclusion of the summit, Moon and Kim signed a joint declaration pledging to work toward “complete denuclearization, a nuclear-free Korean peninsula.”

Diplomacy with the North continued through 2019, with high hopes pinned on a February meeting between Kim and Trump in Hanoi, Vietnam, that observers believed might lead to the normalization of relations between the U.S. and North Korea. That summit collapsed almost as soon as it began, but it led to renewed discussions in the South about restoring rail lines with the North and exploring other joint commercial enterprises. While the U.S. remained conciliatory with the North, it adopted a transactional stance with the South, demanding that Seoul more than quadruple its financial contribution to the cost of maintaining the U.S. presence in the country. Although the South Korean public remained broadly supportive of the U.S.–South Korea alliance, such a concession would have been political poison for Moon. He rebuffed the Trump administration’s request and ultimately agreed to a funding increase of less than 10 percent.

South Korea’s 2022 presidential election was won by Yoon Suk-Yeol of the conservative People Power Party, who had served as prosecutor-general during the Moon presidency. The primary policy changes of his presidency have been a hardline attitude toward North Korea, in contrast to Moon’s more conciliatory and open attitude toward the North, and a deepening of South Korea’s alliances with the U.S. and Japan. Otherwise, his presidency has been largely defined by unpopular domestic policy proposals, such as a school reform that would have sent children to kindergarten at the age of five instead of six and an attempt to increase the maximum hours in a workweek from 52 to 69.

The National Assembly elections in April 2024 were largely perceived as a referendum on Yoon’s presidency, and the liberal opposition parties won a landslide victory, securing 175 out of 300 parliamentary seats. This clearly demonstrated Yoon’s unpopularity and prompted Prime Minister Han Duk-Soo and Yoon’s top presidential aides to offer their resignations. Although Yoon’s presidential term does not conclude until 2027, it seems likely that he will leave office having made relatively little impact because of an opposition parliamentary majority for the entirety of his tenure.