Martial Law in South Korea Tests Biden and a Key U.S. Alliance

• Dec. 3, 2024Updated 1:43 p.m. ET

For decades, South Korea has been one of the most important U.S. allies in Asia — not only because nearly 30,000 American troops are stationed there, but because it stands as a beacon of democracy in a region where powerful authoritarian nations vie with democratic ones.

President Biden has put a special emphasis on South Korea, choosing it as the first non-U.S. site for his annual international conclave, the Summit for Democracy. And in 2023, he hosted President Yoon Suk Yeol for a state dinner at the White House, where the tuxedo-clad Mr. Yoon sang “American Pie” to an adoring audience. Mr. Biden has also relied on Mr. Yoon to provide munitions for Ukraine’s defense against the Russian invasion.

Now, with Mr. Yoon imposing martial law after wildly accusing the opposition party of conspiring with North Korea to undermine him, the American alliance with South Korea faces its biggest test in decades. And Mr. Biden, who has used democracy versus autocracy as a defining framework of his foreign policy, will have to make hard choices on how to handle the crisis, after years of cultivating relations with Mr. Yoon, a conservative leader, and enhancing military ties to better counter China, North Korea and Russia.

Mr. Yoon’s move appeared to catch the Biden administration by surprise.

On Tuesday afternoon in Washington, hours after Mr. Yoon made his shocking announcement, the White House National Security Council released a terse statement, using an abbreviation for South Korea’s formal name, the Republic of Korea: “The administration is in contact with the R.O.K. government and is monitoring the situation closely as we work to learn more. The U.S. was not notified in advance of this announcement. We are seriously concerned by the developments we are seeing on the ground in the R.O.K.”

Officials said that aides had briefed Mr. Biden, who was visiting Angola.

There was speculation in Washington that Mr. Yoon might have chosen this moment because the U.S. government is in a transition from the Biden administration to the second Trump one, and because Mr. Biden is overseas. Mr. Yoon, a first-term president who barely won the 2022 election, has a low approval rating among South Korean citizens, and his move against the opposition party and the legislature has echoes of the effort by Donald J. Trump to prevent Mr. Biden from taking office after he won the 2020 election.

At a U.S.-Japan diplomatic event in Washington, Kurt Campbell, the deputy secretary of state and former Asia adviser to Mr. Biden, said that “our alliance with the R.O.K. is ironclad, and we stand by Korea in their time of uncertainty.”