隨著冷戰的結束及蘇聯的解體，美蘇對立的構造瓦解了，使得爆發區域性衝突的可能性與機率增加。為了解決此種不穩定的狀態，聯合國的安全保障功能又無法充分發揮之下，區域性的安全保障機制格外顯的重要。在亞太地區中，美日防衛合作一向為主要的區域性安全保障機制。而美日防衛合作的建立，卻可以追溯至冷戰結束前的美日海上聯合防衛的決定。 一九五一年美日安全保障條約簽定以來，美日同盟即成為亞太國際政治中不可或缺之安定要素，而亞太地區的安全保障由美國獨力負擔。然而，隨著越戰的反省，美國開始降低對海外的軍事介入。為了維持亞太地區的戰略平衡，在美國的要求下，美日兩國開始研議建立美日防衛合作機制，而美日兩國既然以太平洋作為主要的往來通道，則海上聯合防衛便成為主要的核心議題，日本在亞太防衛事務上的角色逐漸重要。 在一九八一年五月的美日高峰會議之後，日本首相鈴木善幸在記者會上表示，日本將分擔一千海里的海上防衛任務。因為一千海里的海上防衛範圍涵蓋了西北太平洋海域，明顯超越了日本的領海，突顯了區域性安全保障的機能。而鈴木首相的發言則更將海上聯合防衛從幕僚的研究案，正式「升格」為對美國的政策承諾。

With the collapse of the U.S.S.R. after the end of the cold war, there is much probability of the outbreaks of wars or violence confrontations among the countries in Asia-Pacific region. In response to the instability, building a security mechanism is of great concern on the overall Asian situation. As the United Nations could not provide security for this region, there is a need to establish a system for protecting the security of the region. However, in Asia-Pacific region, only the U.S.-Japan Defense Cooperation has covered the issue, which could be traced back to the formation of the protection policy of the Sea Lines of Communication. Ever since the U.S-Japan Security Treaty was signed in 1951, the U.S.-Japan alliance has been playing a crucial part in international politics in Asia-Pacific region. On the basis of the treaty, America was responsible for the defense mission to ensure the security of this region. However, after the Vietnam War, America started to reflect on the role the country played among the Far-East countries and decided to reduce the involvement of foreign military affairs. To ensure the stability in the region after the withdrawal of American military presence, the mechanism of the defense cooperation between America and Japan was built under the request of America. As Asia Pacific Ocean was the important area both in communication and for military purpose, the formation of the protection policy of the Sea Lines of Communication in the U.S.-Japan Defense Cooperation became the core, and the role of Japan on the Asia Pacific military affairs drew much more attention than ever.