This dissertation examines an increasingly common phenomenon in the post-Cold War context, the military coalition. At the heart of the dissertation is thus the question: what explains political leaders’ participation and burden-sharing decisions on military coalitions? In tackling the question, two distinct lines of research were brought together; the one based on alliances, the other based on foreign policy decision making. Based on the two lines of research, an explanatory framework was developed that combined the insights of alliance dependence thesis and poliheuristic theory. A set of hypotheses was derived and tested, utilizing a multimethod approach: statistical, case study, and experimental analyses. Overall, the results of applying the multimethod approach is suggestive of the strength of the poliheuristic theory, with a supporting role of alliance dependence thesis, in understanding participation and burden-sharing decisions on military coalitions. Moreover, though in large part the second Iraq War (2003 -) was used as the reference in much of the dissertation, an implicit underlying claim of the current research is that the findings may be extended to any broad context wherein the development of a military coalition may be a possibility.

美國柯林頓總統於1995、1996年所提出《擴大與交往的國家安全戰略》報告指出：「美國國家安全戰略基礎在於擴大市場、民主社群，同時嚇阻與圍堵對我們國家、盟邦與我們利益的廣泛威脅。」。為了這一廣泛目的，美國須維持一個強大的防衛力量與運用有效的外交政策，以提升合作性的安全措施；致力打開外國市場與激勵全球成長；助長海外的民主並促進區域的合作安全等。 　　小布希總統2002年《美國國家安全戰略》報告也將「透過自由市場和自由貿易開啟全球經濟發展的新時期」列為國家安全戰略的一環。2006年的「美國國家安全戰略」重申自由且公平的貿易政策是第一支柱的一部份，透過自由市場和自由貿易來啟動一個全球經濟成長的新時代是其整體戰略之一；另一方面為了終結暴政和促進有效率的民主，工具之一就是締結自由貿易協定，鼓勵各國加強法治、打擊腐敗、落實民主責任。 　　美國的東亞政策可說重回「新現實主義」與「新自由主義」的雙軌路線。東亞經貿的發展與區域經濟的整合，更是讓美國看到延長霸權經濟命脈的新金礦。未來區域內的主導地位，將會取決於中國與美國相互競爭，這個競爭也許會是良性的，各取所需、各有所獲，但是過程中將會顯示這兩個大國經濟發展將在區域內的產生權力消長。 　　美國認為，中國在地緣戰略上是具有實力引起國際權力分配產生重大轉變，因此美國政策必須調和改變去掌控中國，以便維持及促進美國重大利益。但是隨著國際局勢變化，美國對中國的態度趨於務實，摒除與中國聯盟對抗蘇聯的思維，轉為全面性交往，但是強化其與日本等國的軍事同盟關係。 　　推展民主制度雖然不一定是美國的優先要務，但只要機會，美國總是鼓勵各國走向民主，因為美國人普遍認為，民主政體有能力抵擋極權擴張、便於美國行使權利、減少軍事衝突的風險。此論點乃基於民主國家比非民主國家更不願意發動戰爭之想法。在某些菁英人士心目中，保障及推展民主乃是美國重要的道德目標。 　　美國為確保國家利益及國家安全戰略總體指導，後冷戰時期美國在東亞區域經濟、軍事、政治安全等領域維護將更為重視，並力求主導區域安全相關議題制定、運作機制和秩序規範。 / US president Clinton points out a topic “Enlargement and Engagement” in the National Security Strategy Report, it says “United States National Security Strategy is based on enlargement the market and diplomatic social groups, simultaneously deter and stop any threat that will disadvantage out nation and allied nations.” For this general purpose, United States has to sustain a strong defense power and utilize diplomatic to improve the cooperation of security measures, endeavor in open foreign market, incentive global economic growth, diplomatic nations growth, and area security cooperation, etc. 　　President George Bush also point out “use free market and free trading to open the new growth of global economic era” from the National Security Strategy Report in 2002. It restated free and fair trading policy plays a big portion in 2006. Through free market and free trading to initiate a new era of global economic growth is part of the plan. The tool of terminating tyranny and effective the diplomatic is making a trade policy to encourage other nations stop crime and corruption. Play the role of democracy country. 　　United States Eastern Asia policy is back to theory of “neo-realism” and “neo-liberalism” two axis. The development of Eastern Asia Trade and Integration of Area Economic are the new vault for United States to prolong his sovereign rule in economic. The future leading nation of the area depends on China and United States competition. It maybe positive, each gains his own benefits, but the process will show the grow or diminish of these two nations economic growth within the area. 　　United States think that China’s regional strategy is very powerful which makes the change of international power distribution, so that U.S. has to adjust the policy to facilitate the U.S. key interests. But, along the change of international situation, the U.S. attitude with China turns out to be more practical. It changes the idea of allied with China against Soviet to fully engage with China in all perspectives. In addition, it strengths the military allied relationship with Japan and eastern Asia countries. 　　To popularize the democracy is not the first priority of United States. If there is a chance, U.S. will always encourage all countries toward democracy. American think that democratic system can stop the extremity system expand, which ease U.S. use his privilege and reduce military conflict risk. This is based on democratic nation is more unwilling to start a war than any other nations. In certain elites’ mind, that the goal of U.S. ethics is to ensure and improve democratic. 　　After cold war era based on U.S. interest, United States is more emphasize on the Eastern Asia’s economic, military, and political security, and endeavor on leading the area security.