The Pentagon made a point of keeping the annual exercises off the front pages, even as U.S. military leaders including Defense Secretary Jim Mattis saw them as critical to the U.S.-South Korean alliance.
Mattis set an explicit policy of going quiet on North Korea, including on the drills, two months ago, just after U.S. President Donald Trump signaled his willingness to hold an unprecedented meeting with North Korean leader Kim Jong Un.
"I do not want to talk about Korea at all," Mattis told a small group of reporters on March 10 as he flew from Washington, D.C., to the Gulf state of Oman.
On Tuesday, North Korea threw into question the summit between Trump and Kim scheduled for next month, angrily blaming the drills and calling them "an intentional military provocation," North Korea's official Korean Central News Agency (KCNA) reported.
The North Korean announcement upended Mattis' goal of carrying out the drills without intense media coverage. But it also appeared to affirm his concerns about drawing too much attention now to U.S. military activity on the Korean peninsula, which has long vexed Pyongyang.
Pyongyang has viewed the U.S.-South Korean drills as rehearsals for invasion.
In early March, South Korea's National Security Office head Chung Eui-yong said after meeting with Kim that the North Korean leader understood that "routine" joint military exercises between South Korea and the United States would continue in spite of improving relations.
This was widely seen as a major concession by North Korea as the United States seeks its denuclearization, though Pyongyang never publicly withdrew its long-standing demand for an end to the drills.
Mattis made no secret that he feared that talking about exercises could somehow complicate the work of diplomats, something that appears now to have happened regardless of the Pentagon's go-quiet approach.
"What I want you to understand is that right now every word is going to be nuanced and parsed apart across different cultures, at different times of the day, in different contexts," he told reporters in March when asked about the drills.
He said U.S. officials directly involved in the diplomatic effort should be the ones talking about North Korea.
So, the Pentagon kicked off one of its biggest annual air combat exercises, Max Thunder, with South Korea on May 14 without even issuing a statement.
Joshua Pollack, a senior research associate at the Middlebury Institute of International Studies in Monterey, California, said, "It snuck up on me."
Pollack said he only became aware of the Max Thunder drills when the KCNA statement was issued, adding, "They (the Pentagon) have been very low key about everything."
Max Thunder, one of two exercises being conducted, is an annual air combat drill at Gwangju air base involving more than 1,000 forces from South Korea and the United States.
Although KCNA described the drills as the "largest-ever," the Pentagon said they were similar in size to previous years.
"During Max Thunder, U.S. and (South Korean) aircrews have the ability to fly missions in realistic scenarios. This type of training is integral to our ability to safeguard the Korean Peninsula together," a Pentagon spokesman said.
Max Thunder is scheduled to end on May 25 and the other exercise, Foal Eagle, is expected to run until the end of May. The summit between Trump and Kim is scheduled for June 12 in Singapore.
Kim's latest move could be aimed at testing Trump's willingness to make concessions ahead of the summit, which is due to be preceded by a visit to Washington next week by South Korean President Moon Jae-in.
Bonnie Glaser of Washington's Center for Strategic and International Studies think tank said Kim may be being influenced by Chinese President Xi Jinping after two recent meetings with him. The Chinese leader has advocated a freeze in North Korea's nuclear program in return for a freeze in U.S.-South Korean drills.
That concession was previously ruled out by U.S. and South Korean officials.
"The fact this issue is back on the table suggests Xi Jinping may have raised it with Kim, and that Kim is carrying Xi's water," she said.
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