President Barack Obama walks with President Nursultan Nazarbayev of the Republic of Kazakhstan and President Dmitry Medvedev of the Russian Federation at the conclusion of their announcements at the Coex Center in Seoul, Republic of Korea, March 27, 2012. As a part of their commitment to combat the threat of nuclear proliferation and nuclear terrorism, the three leaders announced progress in the trilateral cooperation to eliminate the remnants of past nuclear testing activities at the former Semipalatinsk Test Site. (Official White House Photo by Pete Souza)