In Korea, a New President in the South Vows a Harder Line on the North

SEOUL — Yoon Suk-yeol, the new president of South Korea, was sworn into office in Seoul on Tuesday, using his inaugural speech to make promises to heal political and economic divides at home, to fight for international norms and to offer an ambitious package of economic incentives to North Korea.

Mr. Yoon is taking office at a time when conflict in Ukraine and democratic backsliding around the world have become pressing international issues​. He must also contend with an escalating nuclear threat from North Korea and growing friction between the United States and China, two great powers with which South Korea’s diplomatic and economic interests are deeply intertwined.

Mr. Yoon vowed to meet those challenges by standing up for values like “freedom” and “liberal democracy.”

“We, as global citizens, must make a stand against any attempt that aims to take our freedom away, abuse human rights or destroy peace​,” he said during his inauguration ceremony, held on the lawn of the National Assembly.

Mr. Yoon brings conservatives back to the center stage of South Korean diplomacy, signaling a directional shift in Seoul’s policy on North Korea. His foreign policy team has emphasized enforcing sanctions against the North, in contrast to outgoing President Moon Jae-in, who prioritized improving inter-Korean ties.

Under Mr. Moon, South Korea had avoided “taking sides” in the great-power competition between the United States, South Korea’s only military ally, and China, its largest trading partner. But Mr. Yoon has vowed to align his country more closely with Washington while also mending fractured ties with Japan.

On Tuesday, Mr. Yoon said South Korea was ready to “present an audacious plan that will vastly strengthen North Korea’s economy and improve the quality of life for its people.” He added that such a move would be possible only “if North Korea genuinely embarks on a process to complete denuclearization.”

“The door to dialogue will remain open so that we can peacefully resolve this threat,” he said.

Mr. Yoon, 61, won the March 9 election with a razor-thin margin against his rival, Lee Jae-myung. ​He faces myriad challenges at home, like a Parliament controlled by the opposition and a society rife with political tribalism. Young voters remain disgruntled by deepening inequality​ and sky-high housing prices.

During the campaign, Mr. Yoon was accused of pandering to widespread sentiment against China as well as an anti-feminist movement led by young South Korean men. He also promised to abolish the Ministry of Gender Equality and Women, a move that helped him win votes from young men who say the country has been overrun by angry feminists.

His most urgent crisis, however, is North Korea.

Both United States and South Korean officials have warned that North Korea could resume nuclear tests as soon as this month, probably around the time President Joe Biden is scheduled to meet with Mr. Yoon in Seoul on May 21.

The North has a history of attempting major provocations to challenge a new leader in Seoul. It conducted its third underground nuclear test two weeks before President Park Geun-hye was inaugurated in February 2013. It conducted its first intercontinental ballistic missile test less than two months after Mr. Moon took office in May 2017.

In the weeks that preceded Mr. Yoon’s inauguration, North Korea conducted several weapons tests, including the launch of an intercontinental ballistic missile on March 24, which ended a four-year-old moratorium on ICBM tests.

Over the weekend, Park Jie-won, director of South Korea’s National Intelligence Service, ​told local media that North Korea was preparing a nuclear test​​ despite objections from its allies, China and Russia. The planned test was crucial for Kim Jong-un, the leader of North Korea, because it would allow the country to test a smaller and lighter nuclear warhead that it could then mount on shorter-range missiles aimed at U.S. allies in the region.

“Time is definitely on North Korea’s side,” Mr. Park said. “Its nuclear technology will improve, its facilities will expand, and there will be proliferation. We must stop this.”

Unlike Mr. Moon and former President Donald J. Trump, who each held three meetings with Mr. Kim, President Biden has shown little enthusiasm for direct diplomacy with the North Korean dictator. Mr. Yoon has also taken a tougher stance, calling for reinvigorated annual joint military exercises with the United States. During the campaign, Mr. Yoon threatened “pre-emptive strikes” against North Korea should an attack look imminent.

“There is no way North Korea will accept” Mr. Yoon’s offer to trade economic incentives for nuclear weapons, said Cheong Seong-chang, director of the Center for North Korean Studies at the Sejong Institute in South Korea. “Under the new government, we will very likely see the North Korean nuclear problem deteriorate rapidly.”

The last time conservatives were in power in Seoul — 2008 to 2017 — they offered to provide North Korea with incentives similar to the ones offered by Mr. Moon on Tuesday. North Korea responded by launching some of its most serious military provocations since the end of the Korean War: Forty-six South Korean sailors were killed in the sinking of a naval ship that the South blamed on a torpedo attack from a North Korean submarine.

The North also bombarded a South Korean island with rockets and artillery shells, killing four people. In response, South Korea shut down a joint inter-Korean factory complex and stopped all trade with North Korea.

Over objections from China, South Korean conservatives also embraced stationing the American antimissile defense system known as Thaad in South Korea in 2017. During his campaign, Mr. Yoon promised to deploy another Thaad system in South Korea, risking retaliation from Beijing.

“Yoon Suk-yeol takes office with the external environment stacked against him,” said Park Won-gon, a political scientist at Ewha Womans University in Seoul. “He has to deal with tensions with North Korea. He has to persuade the Biden administration to shake off its lackadaisical stance on North Korea and make it a priority. He has to do the homework Moon Jae-in had left undone, like how to position South Korea in the friction between the United States and China.”

In surveys by Gallup Korea in recent weeks, about 42 percent of respondents said Mr. Yoon was doing a good job as president-elect. His recent predecessors — conservative and progressive alike — came into office enjoying approval ratings of roughly 70 percent.

Mr. Yoon’s first major initiative — his decision to relocate the presidential office to another government building — had more detractors than supporters. And many of his Cabinet appointees have faced already allegations of ethical lapses. One of them, his pick for education minister, resigned last week.

On Tuesday, Mr. Yoon acknowledged “internal strife and discord” in South Korean society, but said the solution was “science, technology and innovation.”

“Rapid growth will open up new opportunities,” he said. “It will improve social mobility, thereby helping us rid of the fundamental obstacles that are aggravating social divide and conflicts.”