1945年7月二戰進入尾聲之際，因著日本接連戰敗，美國總統杜魯門與英國首相邱吉爾（Winston Churchill）在柏林郊外波茨坦會議上便已開始討論戰後治理日本的計畫。在8月6日和9日，美國分別在廣島和長崎投下了兩枚原子彈，此事促使日本昭和天皇於8月10日緊急透過瑞典及瑞士政府向中、美、英、蘇四國照會接受波茨坦公告，不久後日本無條件投降。戰後美蘇二國開始對處理日本問題出現政治理念上的矛盾，美國亦開始尋找能夠箝制蘇聯的基地。日本正好位於亞洲東北隅，它的優越地理位置獲得美國青睞，美國便極力向同盟國爭取單獨管理日本的權利，經過一番努力，日本由盟國共同監管，而以美國取得主導權。 8月28日，駐日盟軍總司令麥克阿瑟將軍開始接管日本，並展開一系列重建日本的計畫。值此同時，遠東軍事法庭成立，其目的為審判戰敗國之相關罪犯，但日本天皇亦被歸為此類，他正等待著法庭的傳喚與審判。而正在此刻，美國政府決定幫助日本保有天皇，這樣做的目的係為取得日本國民的信任，以方便日後管理日本。
從理性行為者模式（Rational Actor Model）的觀點來看，華府堅持戰後應保有日本天皇是根據其派駐在日本的麥克阿瑟將軍，在日本所做的民意調查結果，此份調查顯示，天皇是維繫日本社會和諧不可或缺的一環。易言之，保有天皇可以穩定日本社會秩序，亦可利用與天皇友好而幫助美國更輕易地管理日本。而從組織行為者模式（Organizational Behavior Model）的角度來看，杜魯門總統在戰後對日本政策方面，顯然更信任戰爭部而非國務院。在戰後天皇存廢問題方面，當時負責處理遠東軍事事務的戰爭部比國務院更佔上風，亦是件自然不過的事，戰爭部遠比國務院擁有更多的戰後處理經驗，因此更得總統信任。而在此案例中，國務院與戰爭部對於保有天皇的觀點卻是不謀而合，因此少了雙方諜對諜的激烈鬥爭，但是從細部觀察，仍可窺見杜魯門總統在處理日本事物上顯然更依賴戰爭部。再從政府政治模式（Governmental Politics Model）觀之，副國務卿格魯（Joseph C. Grew, 1880-1965）為杜魯門總統所青睞，格魯曾任駐日大使，其精闢的對日見解，成為美國重建日本經濟與政治的藍圖；而戰爭部底下之遠東軍事總司令官麥克阿瑟（Douglas MacArthur）因為具備專業作戰知識與實地駐紮日本的經驗，其建言又比格魯更容易影響杜魯門的最終決策。儘管麥克阿瑟在後幾年的遠東處事立場上，逐漸與杜魯門產生矛盾，但在1945年面對日本天皇的存廢問題時，他們兩者的關係尚稱和睦。相形之下，國務卿貝爾納斯（Byrnes）雖是總統摯友卻無特殊專業軍事背景，因此無舉足輕重。此外，在規劃處理對日事務的案例中，麥克阿瑟確實比格魯與貝爾納斯又多一份經驗。另外，麥克阿瑟駐紮日本總攬大權，總是越級報告總統，因此他擁有更多接近總統的機會。以上因素促使杜魯門總統體認到，美國如能成功佔領日本並期望從中得益，領導日本成為一個「自由民主」 與一個「資本主義」的國家，將會符合美國利益，而幫助日本保有天皇又使美國得以從中獲利，因此他同意保有日本天皇的決策。
In the wake of the end of World War II in 1945, the United States and the Soviet Union, which were originally belonged to the same camp (Allies), have lost their common enemy—Japan. There were different political ideas between the two giant powers: the United States was a free and democratic country which led the democratic and free countries in the postwar years, whereas the Soviet Union was a Communist regime after World War II. The two superpowers keenly competed with each other in the military or technological dimensions.
Japan’s destiny was uncertain after the World War II. At this point the United States actively strived for the leading authority to control Japan so that it could establish its dominant position in East Asia and closely monitor Soviet behaviors. As a result, the main purpose of this thesis is to understand the process of how and the reasons why the U.S. decided to retain the imperial system of Japan after the WW II.
From the perspective of Rational Actor Model (RAM), this thesis finds that, during the war years, Grew, then undersecretary of State Department, advised President Harry S. Truman to retain Hirohito as a way to make a compromise with Japan, but the president did not agree with him. The main reason behind President Truman was that he demanded an unconditional surrender from Japan. When the World War II was over, Crew’s proposal was presented once again, but the president worried that once the decision of maintaining the imperial system was made, the mainstream opinions of the postwar world would be arisen against him. It was not until General MacArthur sent a telegram to inform the president, by saying “If you are not allowed to retain the emperor, then please you send another one million troops to support here.” It goes without saying that these impressive words made President Truman change his mind. As a result, the president decided to retain the Japanese emperor in order to maintain the interests of the United States and the lives of American soldiers. If a policy option can prove that it pays less and get more benefits, it will be much easily to be adopted.
From the perspective of Organizational Behavior Model (OBM), President Truman was more likely to trust the Defense Department than the State Department because the military organization had more combat experience and expertise than the civilian organization. The president’s preference in this case demonstrates that the stronger capabilities an organization owns, the easier its views will be adopted.
From the perspective of Government Political Model (GPM), it is quite clear that although the president has the final say in the decision-making process, an important official who have frequent access to the president will influence the judgment of the president. General MacArthur often reported to Truman directly regardless of the hierarchical red tape. In this way, he significantly increased the interaction between the president and him. It suggests that even the president has the final say, an official who has more action channels will get his way to have his policy option adopted.
Personally I believe that the American stance in retaining the Imperial system was also significantly influenced by the attitude of the Japanese Imperial Palace Group (including the Emperor himself). In his memoirs, General MacArthur greatly praised Emperor Hirohito who in turn accommodated to the requests of the U.S. government. The benign interaction between the Japanese Emperor and the U.S. government demonstrate the strategic goals and motivations of the United States to retain the imperial system for Japan. Therefore, the main theme of this thesis is that the United States decided to retain the imperial system because it wanted to maintain its leading authority to control Japan so that it could not only establish its dominant position in East Asia but also closely monitor Soviet behaviors from the perspectives of RAM, OBM, and GPM.