標題：薩德之辯凸顯韓兩難困境

　　South Korea is on two front lines. One is as a key ally of the US, with US forces still based on its territory and mutual treaty obligations, despite the fact that it is also economically directly in China's sphere of influence. Like many others in the region it has to increasingly balance its security interests with its economic ones. But unlike many of them, in terms of proximity it is one of the closest and most integrated into the Chinese economy. The second line it occupies is with North Korea along one of the world's most volatile and unresolved borders. Its vulnerability against attack from the North has been a constant feature of its security situation since the war in 1950-1953, and frames much of its security thinking.

　　Balancing these relationships of the US and China in view of its unique situation has never been easy. During the early 2000s, especially at election time, constituencies in South Korea wanted more distance from the US, and greater autonomy. They felt resentful at the continuing presence of US forces on their territory. Anti American demonstrations were common, and sometimes politicians played to this. In recent years this has been accompanied by warm overtures from China, with trade and investment flowing between the two. South Korea's growth has become more dependent on China with the weakening of US and other developed economies from 2008 and the Great Financial Crisis.

　　The simple fact however is that any South Korean leader who wants to put too much distance with the US immediately risks being accused of making the country vulnerable to security threats from North Korea. North Korea's unpredictability remains, ironically, the most predictable thing about its behaviour. Its increasing nuclear capability and its internal leadership instability in the last four years in particular, after the death of Kim Jong Il, have only intensified South Korea's security dilemma. It needs to be part of the US security blanket, because it cannot trust either the DPRK, or a country seen as its key ally China, to look after its interests. It is in a tough neighbourhood, and the US still offers it the best deal.

　　Part of that deal might include acquiring the Terminal High Altitude Area Defense (THAAD) system, a defensive system from the US that would protect South Korea against ballistic attack. Talks have reportedly been ongoing since 2014 about this, though both sides have denied they have been formal. THAAD acquisition is a sensitive subject because it touches on South Korea's relations with its two most important allies. It runs the risk of alienating one at the expense of another. It forces on South Korea a choice. This may carry diplomatic costs.

　　There are two related issues here. The first is that the threat of ballistic attack from North Korea on the South is not a fantasy. It is very real. North Korea has had one of its few successes in ballistic missile technology, with a number of short to medium range missiles that are perfectly capable of reaching into the south and causing widespread damage. In the past it has fired missiles across Japan. Having the ability to deter these would be a critical issue for South Korea.

　　But, as always, there is a wider dimension, bringing us to the second issue. Chinese military and political leaders have made it clear that they regard the supply or THAAD as another sign of the US increasing its military involvement in the region. It fits into the narrative of US containment that has been an increasing part of Chinese thinking since President Obama became president in 2009. China feels that the Korean peninsula is a crucial part of its sphere of influence, and that the US supplying such high tech equipment, while ostensibly for threats from one country, is directed at them.

　　China's attitude to North Korea has certainly undergone some changes in the last two years since Xi Jinping came to power. There have been clear signs of frustration by Beijing in the mercurial leadership in Pyongyang, especially over the execution of one of Kim Yong-un's uncle, seen as a pro Chinese voice in the elite leadership, two years ago. Xi broke with precedent and went to South Korea last year, but has so far not visited the north. In the past, visits to the North took precedence.

　　South Korea has to balance asserting its own interests against causing some ruptures with its most important regional neighbour. The main calculation is whether THAAD can give it security, without carrying a political costs of alienating Beijing in the long term, and causing it to be tied even more closely to the US. It wants autonomy, rather than further ties, but it also wants to know it had the best capacity to deal with a north that harbours such aggressive intent towards it.

　　Diplomacy is about finding ways between tricky, competing demands. It is about getting an outcome that supports a nation's self interest while letting it maintain the best relations with the outside world. Part of South Korea's self interest is clearly served by having optimal relations with China. But that might not take precedence over having the best possible defence system. The best outcome would be to convince China that, in fact, it having this capacity would also be in its interests. It would mean a more secure, stable environment. Surely that is in China's interests too. The question now is whether South Korean diplomacy is up to this task.

　　Professor Kerry Brown

　　Kerry Brown is Professor of Chinese Politics and Director of the China Studies Centre, University of Sydney and Team Leader of the Europe China Research and Advice Network (ECRAN) funded by the European Union. He is an Associate Fellow of Chatham House, London and author of `Struggling Giant: China in the 21st Century' (2007), `The Rise of the Dragon: Chinese Inward and Outward Investment in the Reform Era' (2008), `Friends and Enemies: The Past, Present and Future of the Communist Party of China' (2009), `Ballot Box China' (2011), `China 2020' (2011), `Hu Jintao: China's Silent Leader'(forthcoming).