After a year of frosty diplomacy and economic pressure, South Korea and China announced Tuesday that they would put aside their differences out of a joint desire to denuclearize the Korean Peninsula.

South Korea’s Foreign Ministry said the two countries will resume normal relations. “The two sides attach great importance to the Korea-China relationship,” a statement from the ministry said.

In its own coordinated statement, China’s Foreign Ministry said the two nations would work to put their relationship back on a normal track “as soon as possible.”

China and South Korea have historically deep ties and over the past few decades had enjoyed a close relationship. However, that relationship was deeply damaged last July when Seoul agreed to install the U.S.-owned Terminal High Altitude Area Defense (THAAD) missile defense platform on its land.

Though both Seoul and Washington argued the THAAD system had only defensive capabilities, Beijing was concerned about U.S. encirclement as well as the system’s sophisticated radar capabilities.

Chinese President Xi Jinping was also angered that former South Korean president Park Geun-hye had sided with American interests over China, said Yun Sun, a senior associate with the East Asia Program at the Stimson Center.

“Xi had tried to sway South Korea’s alignment choice, and when Park rejected China’s demand not to deploy THAAD, it made Xi’s great diplomacy on South Korea a failure and an embarrassment,” Sun said in an email this weekend.

When the missile system was deployed earlier this year, China’s Foreign Ministry spokesman, Geng Shuang, warned that Beijing would “resolutely take necessary measures to defend our security interests.”

South Korea’s Foreign Ministry acknowledged that the THAAD dispute had not been fully resolved. “The two sides agreed to engage in communication on THAAD-related issues about which the Chinese side is concerned through communication between their military authorities,” it said in a statement.

For its part, China confirmed Tuesday that its position on THAAD had not changed.

And on Sunday, South Korea’s military chief met with his American and Japanese counterparts, as part of a growing three-way dialogue.

China is South Korea’s largest trading partner, and it used this economic clout to punish Korean businesses when the antimissile system was deployed. Trips by Chinese tour groups to South Korea were suspended, with the number of Chinese visitors dropping 60 percent in the first nine months of the year compared with 2016, according to figures released by the Bank of Korea.

Korean-owned businesses also suffered boycotts and bans in China. The situation was especially difficult for the Lotte conglomerate, which had allowed its land to be used for the installation of the THAAD system. Last month, it announced it would be selling off its supermarkets in China after most were shut down for fire code violations and other alleged infractions.

President Moon Jae-in's new South Korean government had recently made a number of moves to ease China's anxiety over THAAD, with Foreign Minister Kang Kyung-wha announcing last week that South Korea would not seek any more deployments of the system. The moves had been received warmly in China's state-run press, with the nationalist Global Times newspaper saying that the "proactive" stance of Moon's government was "a new gesture that is welcomed."

Choi Kang, vice president of the Seoul think tank Asan Institute for Policy Studies, said that South Korea had not offered any real concessions on the issue. “Since South Korea has maintained a very firm position on THAAD, the Chinese side decided to move instead,” Kang said.

Instead, North Korea and other factors may have led to the agreement between the two nations, which came after the Chinese Party Congress that saw Xi consolidate his power over the country and exactly a week before President Trump arrives in South Korea as part of a 12-day Asia trip.

China is keen to restart relations with South Korea under Moon, said Sun, as he has signaled that he is seeking an independent policy and is open to talks with North Korea, a long-standing ally of Beijing. “When the relationship with President Park was beyond repair for China, Moon gives China new hope,” Sun wrote.

However, Kang said that the two sides still had different outlooks on the region that could lead to more disputes. China and South Korea felt the “necessity to manage their bilateral relations for different reasons, not for common objectives and concerns,” Kang said. “The conflict is not over yet.”

North Korea’s provocations have prompted other shifts in the Pacific, as well. In one example, the senior military officials from the United States, South Korea and Japan are incrementally increasing collective ballistic missile defense, despite strained relations between South Korea and Japan that date back to Japan’s invasion of the Korean Peninsula during World War II.

On Sunday, Marine Gen. Joseph F. Dunford Jr., the chairman of the Joint Chiefs of Staff, met with his South Korean counterpart, Gen. Jeong Kyeong-doo, and their Japanese equivalent, Adm. Katsutoshi Kawano, at the sun-drenched headquarters of U.S. Pacific Command in Hawaii.

The Japanese and South Korean defense chiefs have narrowly increased military dialogue with each other as it relates to North Korea, meeting five times since July 2014 in three-party talks with Dunford and his predecessor, Army Gen. Martin E. Dempsey. On Sunday, the agreed to hold quarterly missile defense exercises in 2018, Dunford said.

Dunford said that the discussions between South Korea and Japan are important for a couple of reasons.

"Number one, from a deterrence perspective, it's important that Kim Jong Un and [North Korea] see that they are facing a collective response from the international community, and in particular, those nations most affected," Dunford said. "And number two, if we do have to respond, Japan is a critical ally that the United States is going to need to meet its alliance commitments. We have over 50,000 forces in Japan. It is a platform from which we would project power in any South Korean response."

Correction: An earlier version of this story inaccurately cited the World Bank as the source of figures on Chinese visitors to South Korea. The figures came from the Bank of Korea, and the story has been corrected.

Simon Denyer in Beijing and Dan Lamothe in Washington contributed to this report.

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