頂尖強權間之衝突與合作，是國際關係學界的核心議題。強權戰爭往往造成生命財產的重大損失，其影響範圍更遠及於交戰國疆界之外。第二次世界大戰就是鮮明的案例，而其後的美蘇對峙，也讓世界瀕臨毀滅性核戰邊緣。美蘇冷戰終結後不久，中國大陸便成為世上僅次於美國的強權，而華府與北京之間的關係隨之變成世人關注的焦點。傳統的國際關係理論，能否解釋頂尖強權間的關係？ 本研究檢驗了一六六○到二○○六年，國際政治體系中最強的兩個國家間的衝突與合作，發現下列事實：一、第二強權與第一強權的權力比值愈大，則衝突傾向愈低。這與權力平衡論的預期相符，但與權力移轉論的預期相反。二、兩個民主強權之間的衝突傾向偏低。三、經濟發展水平愈相近，衝突傾向愈高。四、在兩強皆擁有核子武器的情形下，衝突傾向偏高。五、領土相鄰會提升衝突傾向。六、在上述五個因素中，政體與權力這兩個因素的影響力最大。

Conflict and cooperation between the two most powerful countries is a core issue in the field of international relations. A war between two powerful nations usually causes serious loss of life and property, with further implications far beyond the boundaries of the combatant states. The Second World War is a vivid example, and the subsequent U.S.-Soviet rivalry led the world to the brink of nuclear destruction. Not long after the end of the Cold War between the United States and Soviet Union, China became the second strongest power in the world, with overall national capabilities inferior only to those of the United States. As a result, the relationship between Washington and Beijing is the central focus within the international arena today. Can traditional IR theories adequately explain relations between these “greatest powers”? By examining conflict and cooperation between the two most powerful states in the international political system from 1660 to 2006, the author finds the following: first, the higher the power ratio between the second largest power and the largest one, the lower the tendency for conflict between them. This finding is consistent with balance-of-power theory, but contradicts power transition theory. Second, the tendency to conflict between two democratic powers is low. Third, a lower economic developmental gap leads to a higher tendency to conflict. Fourth, the tendency to conflict is high between two nuclear powers. Fifth, geographic proximity increases the tendency to conflict. Sixth, among the above five factors, relative power and regime type are the most important.