"South Korea (known officially as the Republic of Korea, or ROK) is one of the United States' most important strategic and economic partners in Asia, and since 2009 relations between the two countries arguably have been at their most robust state in decades. Members of Congress tend to be interested in South Korea-related issues for a number of reasons. First, the United States and South Korea have been treaty allies since the early 1950s. The United States is committed to helping South Korea defend itself, particularly against any aggression from North Korea. Approximately 28,500 U.S. troops are based in the ROK and South Korea is included under the U.S. 'nuclear umbrella.' Second, Washington and Seoul cooperate in addressing the challenges posed by North Korea. Third, the two countries' economies are closely entwined and are joined by the Korea-U.S. Free Trade Agreement (KORUS FTA). South Korea is the United States' sixth largest trading partner and the United States is South Korea's second-largest trading partner. South Korea has taken the first steps toward possible entry into the U.S.-led Trans-Pacific Partnership (TPP) free trade agreement negotiations. […] The United States and South Korea signed a new civilian nuclear cooperation agreement in mid- June 2015 to replace the existing agreement, which entered into force in 1974. The agreement, which provides the legal foundation for nuclear trade between the countries, automatically will go into effect in the fall of 2015 unless Congress disapproves it, a move that would be subject to presidential veto."
CRS Report for Congress, R41481
Federation of American Scientists: http://www.fas.org/sgp/crs/index.html