由於北韓的軍事威脅，國家安全一直是影響南韓政治與外交的首要變數。冷戰時代南韓保守右派政權皆視北韓為首要敵人，內政上防範北韓滲透顛覆，外交上則以對抗北韓為主。因此如何維持與美國的軍事同盟成為南韓外交與安全的首要目標。然而1987年民主化與1997年金融危機使自由主義取代保守主義成為南韓政治主流。本文主旨在檢視南韓民主化與國家安全的關聯性，尤其是民主化所帶來自由主義思潮的興起對南韓人民安全觀所造成的衝擊及其對韓美軍事同盟的影響。作者發現自由主義的思潮使南韓人民降低對北韓的敵意、增加反美情緒。韓美安保合作在小布希上台以來裂痕加深，固然與南韓境內自由派興起有關，但是小布希政府濃厚的新保守主義作法才是真正導致南韓輿論反美，韓美同盟發生危機的關鍵。因為南韓總統金大中與盧武鉉皆力圖維持與美國的友好關係，儘量調適與彈性處理與美國在理念與政策上的歧異，凸顯南韓主政者是理性而務實的。

Because of North Korea's military threat, national security has been the most significant variable affecting South Korean politics and diplomacy. During the Cold War period, South Korea's rightist regimes viewed North Korea as archenemy, so their policies were designed to prevent North Korea's penetration and subversion domestically and to contain North Korea internationally. Hence, how to maintain military alliance with the U.S. was the first priority in South Korea's foreign and security policies. However, democratization in 1987 and the Asian financial crisis in 1997 brought about the emergence of liberalism that replaced conservatism as the mainstream of South Korean politics. The theme of this paper is to examine the linkage between South Korean democratization and national security, in particular the impact of rising liberalism on South Korean's perception of security and ROK-US military alliance. The author finds that emerging liberalism has resulted in lowering South Korean's hostility against the North as well as increasing the sentiment of anti-Americanism. ROK-U.S. security cooperation has further drifted apart since George Bush assumed his presidency. Though this is related to rising liberalism in South Korea, the Bush Administration's neo-conservative approach is the primary cause of surging anti-American sentiment and undermining ROK-US military alliance. Both South Korean Presidents Kim Dae-jung and Roh Moo-hyun have tried their best to adjust themselves to Bush's tough North Korea policy and to deal with their ideological and policy differences in a flexible manner. It is a retlection of South Korean leaders' pragmatism and rationality.