Throughout his 40-year diplomatic career until December 2021, Sungnam Lim was constantly involved in the ROK-US alliance in one way or another. He spent about 12 years working or studying in cities such as Washington DC, New York, and Cambridge MA. At the Foreign Ministry, he served as Senior Coordinator for ROK-US Security Cooperation as well as Director of North America Division I and III. While he was serving as Ambassador for the North Korean Nuclear Issue and then Special Representative for Korean Peninsula Peace and Security Affairs, the ROK-US coordination was always at the top of his agenda. Recently, when he was First Vice Foreign Minister from October 2015 to September 2018, he also focused on the ROK-US cooperation with the then Deputy Secretary Tony Blinken bilaterally or trilaterally with Japan. In addition to the US, Ambassador LIM served in London, Beijing, Taipei, and Jakarta, and studied in Tokyo.