No...but ostensibly the UN may as well have been up and running by 1944 considering the deal-making and preconceived re-alignment of European borders between FDR, Roosevelt, and Stalin.
My point - the last "war" the US fought to win was WWII.
A few background links on our relationship with South Korea for those interested:
Shock Poll - South Koreans Prefer North Korea To The United States (Feb 2006)
http://blogcritics.org/politics/article/shock-poll-south-koreans-prefer-north/
Survey: Americans question role in Korean peninsula
http://www.cnn.com/2010/US/11/23/americans.south.korea/
One of America’s Strongest Allies, and Why it Gets Overlooked
http://www.buzzle.com/articles/one-of-americas-strongest-allies-and-why-it-gets-overlooked.html
South Korean Anti-Americanism (2003)
http://www.jpri.org/publications/workingpapers/wp93.html