Last week, the United States began deploying the Terminal High-Altitude Area Defense (THAAD) to South Korea. The anti-ballistic missile system is intended to counter a North Korean security threat. Designed by Lockheed Martin, it will connect with the wider US missile defense system to counter short-, mid-, and long-range ballistic devices at the terminal stage with an interceptor, often likened to “hitting a bullet with a bullet.” Deployment—which is slated to finish by the end of 2017—has incited debate about technical capabilities, which has increasingly disrupted regional politics as China and Russia seek to stop THAAD. The departure of South Korean President Park Geun-hye has further complicated the strategic calculations of all parties.

China has long been vocal about its opposition to THAAD deployment to the region. It fears that the radar system could be used as an early warning to US missile defense batteries elsewhere, thereby decreasing the nuclear deterrence capability of China in the event of military confrontation with the US. American analysts argue that the range of THAAD radar cannot reach into China with enough accuracy to warrant these concerns.

As I have previously discussed on the Global Observatory, China has framed the THAAD decision as a “strategic choice” that represents South Korea betraying its relationship with China. Since the decision in July, Beijing has already exhibited signs of economic retaliation against Seoul: Korean pop and classical music tours scheduled in China have been canceled, and Korean television shows—one of Korea’s largest exports to China—are no longer being aired.

In January this year the Chinese government began rejecting applications for charter flights between South Korea and China, while Eastar Jet (a South Korean budget airline) temporarily suspended flights to three destinations into China last week. Jin Air (a unit of Korean Airlines) is also reviewing some flights into China. As of last week, the Chinese government has reportedly closed nearly half of the stores of Lotte Mart, a Korean retail chain, in China—some citing fire safety concerns—and Chinese patrons, riding a wave of anti-Korean sentiment, are boycotting the remaining stores.

Though no official reasons have been given, the cancelations and application rejections appear to be as part of an effort to counter the THAAD decision. The Korean government is mulling over whether to file a complaint against China in the World Trade Organization, on the grounds that the retaliation could be considered as violating the terms of its bilateral free trade agreement.

Russia, meanwhile, has also voiced opposition to THAAD. Early last month, the Russian ambassador to South Korea, Alexander Timonin, told reporters in Seoul that Russia sees THAAD as a destabilizing element in Northeast Asian relations and an impediment to North Korean denuclearization. He said that THAAD deployment affects Russia’s policy to the region and could damage bilateral relations.

The two great powers’ concerns are amplified by their unification. The China-Russia nexus is a formidable one, as both countries are key to regional security. Taking a longer view, they are also key to the trajectory of unification of the Korean Peninsula.

On February 28, China’s Assistant Foreign Minister Kong Xuanyou hosted Russian Deputy Foreign Minister Igor Morgulov, to discuss the tensions and security in Northeast Asia more generally. The two diplomats serve as co-chairs of the Russia-China dialogue on regional security. A Russian statement following the meeting said that both sides believe “that collective political and diplomatic efforts should be stepped up to ease tensions and initiate the process of military and political detente across the board in Northeast Asia, in order to create conditions conducive to resolving the nuclear issue, as well as other issues, on the Korean Peninsula.”

Chinese and Russian concerns could be further aggravated by the recent revelation that the Pentagon has, for the past three years, been using cyber and electronic strikes to thwart North Korea’s missile program. An investigation by the New York Times, published March 4, suggests that the US cannot reliably counter the North Korean missile and nuclear programs. North Korea has been stepping up the frequency of missile testing since Kim Jong-un taking leadership in 2011, but the test results have been inconsistent and rocky. Some analysts suggest that the cyber-strikes are responsible for truncated trajectories or unplanned explosions, while others allege the missile tests are inherently inconsistent and risky.

Turning to South Korea, last week’s unanimous Constitutional Court ruling in favor of Park Geun-hye’s impeachment means leadership turnover within the next two months. The THAAD issue has long been a domestic political football, particularly as the South Korean electorate fears continued economic retaliation from China. While the US is largely recognized as the country’s most important security partner (63% believe the US is the most important, while 12% believe it is China), most Koreans see China as more important in terms of its economic relations—56% chose China in this respect, compared to the 32% who identified the US.

Taking a broader strategic view, according to an annual poll conducted last year, most South Koreans (57%) recognize their country’s relationship with China as cooperative rather than competitive. Yet there are indications of changing opinions in this respect—the year-on-year percentage viewing the relationship as competitive increased from 32% in 2015 to 38% in 2016. Moreover, this pales in comparison to the South Korean view of the relationship with the US, which 86% viewed as cooperative in 2016, up from 81% the year prior.

Opposition party politicians have opposed THAAD deployment during debates and the decision to proceed with it in July last year. The main opposition party focused on the missile system’s significance in drawing sharper attention to Korea’s position between growing US-China rivalry.

In October 2016, Moon Jae-in—the opposition party candidate currently leading the polls for the upcoming presidential election—urged the government to cease deployment procedures pending constitutional review. He also called for more diplomatic efforts to denuclearize North Korea, suggesting that “national interest” is being too narrowly defined. However, continued missile and nuclear weapons testing in North Korea has increased the threat perception among South Koreans, and Moon has since flipped his position on THAAD, indicating that deployment could be delayed but should not be stopped.

South Korea is in a very difficult position: Going back on the decision to deploy THAAD would not only put a dent in its relationship with the US, its treaty alliance partner, but might also diminish its (rhetorical or material) position in deterring and/or negotiating disarmament vis-à-vis North Korea. At the same time, Chinese and Russian concerns—and their resolve to coordinate efforts to halt THAAD deployment—cast a massive shadow over increasingly tense Korean Peninsula relations.

Darcie Draudt is a PhD student in Political Science at Johns Hopkins University and a non-resident James A. Kelly Korean Studies Fellow at Pacific Forum CSIS.