冷戰結束，使得美國全球安全環境發生了歷史性的巨變，在中共快速崛起，區域軍力與經濟力的發展愈形失調之際；從北韓核武威脅、台海主權爭議，到區域民族主義、分離主義與恐怖組織的推波助瀾，將原已嚴峻的亞太情勢推向更為複雜的形勢。基於全般世局的變因與發展，誘發吾人從事國際關係研究的動機，除期望取得一般性國際關係理論與實際知識之外，更期望就小布希政府主政前後美國全球、亞太戰略的主要政策內容，去嘗試發現東亞戰略之理論依據與其關聯性，俾利於我國防政策與戰略發展之研究參考。 經研究發現，促成美國戰略轉變的根源係在不同時空的敵情威脅、全球政經安全情勢與美國內部的政治等因素上；故如何審時度勢，厚植實力，睥睨時局，也就成為美國主導戰略發展的關鍵。 研究也發現，美國東亞安全戰略是其全球、亞太戰略與整體外交、安全戰略設計的一環。冷戰結束後，歐洲呈現安全穩定發展，亞洲則因中共國力竄升與北韓核武危機等新的威脅，既影響東亞區域的平衡穩定，且衝擊到美國的國家利益，迫使美國必須對其東亞安全戰略作出因應的調整，以持續維持美國在世界的領導地位。 「九一一事件」後，促使美國戰略做了重大的改變，對其東亞安全戰略的建構，也針對不同的威脅來源與挑戰，做出國家安全戰略與區域安全戰略的調整和強化；而兩岸三邊關係也出現了若干的調整，從歷史之觀點分析，美國之台海政策基本係依戰略環境之需求而變遷，故台灣如何因應美國戰略之轉變，調整戰略思維，落實「有效嚇阻、防衛固守」戰略構想，達到「預防戰爭」、「維持台海穩定」、「保衛國土安全」之國防目的，實為當務之急。 / Due to the end of cold war, the role of the US in global security environment occurred historic changes. The issues of the North Korea nuclear weapon’s threat, the Taiwan’s sovereignty dispute, regional nationalism, separatism and terrorist groups surged the severe situation of Asia Pacific region more complicate. Owing to the overall variants and developments of the world, I am motivated to study international relation. I expect not only to consume general international relation theory and genuine knowledge but also to explore the theory’s basis and connections of East Asia strategy from those primary policies of the US global and Asia Pacific strategies before and after President George W. Bush assumed his office. This study may useful to the research and reference in our national defense policy and strategy development. Through the study, we discover the fountainheads of promoting the changes of the US strategy are the causes of enemy’s threat, global political & economic security situation and the US domestic politics. So, how to evaluate the world trend, build up immense capability and overwhelm the present posture of affairs become the key factors for the US to lead the strategic development. According to my study, we also discover the US’s East Asia security strategy is a part of its global, Asia Pacific strategies and strategic designs of overall diplomacy and security strategy. After cold war, the Europe develops safely and steadily. But in Asia, the unprecedented threats from the arisen PRC national power and North Korea nuclear weapon’s crisis affect the balance and steady of the East Asia, also pose great influence to the US interests. Thus, the US is forced to make certain adjustments on the East Asia security strategy for dealing with those aforementioned issues in order to maintain its leading status in the world. Post “September 11, terrorist attack”, the US made significant changes on its strategies. The US adjusted and strengthened its national and regional security strategies on East Asia security strategy construction and different threat resources and challenge. Also the US is induced to adjust trilateral relations with Taiwan and China. The US basic policy toward Taiwan Straits, analyzed from historical viewpoints, is changed by the strategic environment need. The ultimate work of Taiwan now, is to response the changes of the US strategy, adjust strategic thinking, fulfill the strategic concepts of “effective deterrence, solid defense” to achieve the national defense goals of “prevention of war”, “maintaining stabilization in Taiwan Straits” and “defending homeland”.