9 August 2016 Author: Sarah Teo, University of Sydney and RSIS South Korean Foreign Minister Yun Byung-se once again defended the deployment of the Terminal High Altitude Area Defense (THAAD) missile system on the Korean peninsula in a meeting with his Chinese counterpart Wang Yi in late July. Wang responded that Seoul’s decision had ‘harmed the foundation of mutual trust’ between their two countries. South Korea’s Foreign Minister Yun Byung-se is surrounded by media after a meeting at Japan’s Prime Minister Shinzo Abe’s official residence in Tokyo, 22 June 2015. (Photo: REUTERS/Issei Kato). South Korea has achieved remarkable successes in its pursuit of ‘responsible middle-power diplomacy’. It has been recognised as a leader, bridge, agenda setter and activist on the global stage — roles commonly associated with middle powers. Yet as Wang’s comments show, Seoul has been less successful in its regional diplomacy. Can Seoul reconcile its ambition to be a middle power on the glo