Geopolitical Considerations.
South Korea with its population of 48 million is located in the center of Southeast Asia. Its geographic and cultural ties to North Korea make it a critical player in the current North Korean nuclear crisis. Both the US and the ROK share strong economic and cultural ties. Korea also shares a history of tributary relations with China in the years before the Japanese occupation of Korea. This history might play a role in the future of the relationship if the US lessens it role in the alliance.
Current Issues.
In 2002 North Korea announced that it was withdrawing from the 1994 Agreed Framework. It confirmed it had begun processing uranium, which is a critical component in creating nuclear weapons. The CIA has long held that it is possible that NK has at least 2 WMD. Multilateral talks have been held since then and North Korea refuses to comply with any inspections or international interference concerning their nuclear program without a non-aggression treaty with the US. The US refuses this on the basis it is being blackmailed by the untrustworthy North Koreans. South Korea believes this attitude is hindering reunification by belittling the Sunshine policies of engagement with North Korea. South Korea believes the policies are succeeding in creating a more peaceful Korean peninsula. The US is setting its eye on North Korea and the threat it poses, while South Korea is focusing on stabilizing its economy and government. .
Also at issue is the current wave of anti-Americanism in the ROK. The current president of South Korea, Roh Moo-hyun beat Lee Hoi-chang on a campaign that was critical of current US policy toward North Korea. However in the days of lagging US support for the war on terror internationally, South Korea has been a firm supporter since 9/11.
US interests in order of importance considering US relationship with SK in NK context.
Fight against international terrorism.