本論文研究結果發現，亞太區域內的問題與美日聯盟之間的問題激化，雖然對美日同盟關係產生了影響，使美日兩國勢必重新調整彼此的合作關係，然而新威脅的出現則促成了美日聯盟的提升。朝鮮半島的問題讓雙方確認了美日同盟關係的重要性，中共崛起問題再度讓兩國體會了提升美日聯盟的重要性與急迫性，台海危機讓美日同盟重視到台灣問題的重要性，而恐怖主義的出現更是催化了美日同盟在亞太區域安全上的維護與合作，這些作為當然是為了讓兩國更有效率地來共同應付新威脅，美日雙方於二加二聲明中，展現出同盟的決心與態度。在進入廿一世紀的美日同盟關係上，一九六○年的美日安保條約仍是兩國合作關係的主要基礎，但在彼此的責任義務分配方面，則是朝向趨於更平等的方向上邁進。 This thesis is mainly focus on the alliance theory. U.S.-Japan alliance has been existed over 50 years. In the 21st century, it faces new challenges which can improve the relationship between the two countries.
The findings of this thesis are as follows:
The change of the international relationship, and the problem of Okinawa were really to some degree harmful to the U.S.-Japan relationship in a certain degree, and made it become inevitable for these two countries to reshape their alliance; however, the emergence of new challenges, made both decide to cooperate with each other more closely.
U.S. and Japan acknowledged the importance of their defense cooperation when the nuclear crisis in the Korean Peninsula developed. The case of China Rising and Taiwan Strait issue also made U.S. and Japan awake to the urgency of promoting their alliance. In order to deal with these new threats more effectively, these two countries had good communication- “The 2+2 talks.” In the 21st century, the Treaty of Mutual Cooperation and Security Between the United States of America and Japan (1960) still remains as the foundation of this bilateral relationship, but the distribution of the responsibilities in the U.S.-Japan alliance has become more and more equal.