從攻勢到守勢：權力平衡、觀念轉變與澶淵之盟的形成

From Offensive to Defensive: Balance of Power, Change of Ideas, and the Formation of Chanyuan Covenant

為什麼兩個大國可以擺脫長期戰爭，轉為和平相處？結構現實主義者認為這要靠物質力量的平衡，而建構主義者提醒我們不能忽略觀念因素。本文藉由「杰維斯」（Robert Jervis）與「李維」（Jack S. Levy）關於學習的兩階段模式整合物質與觀念因素，以澶淵之盟為例，敘述宋遼雙方如何先取得足以自保的物質基礎，然後再進一步擴張的過程中遭遇有能力自保的對手。在發動不只一次不成功的攻勢後，遼、宋決策者終於認知到彼此勢均力敵，並歸結出「進攻不再有利可圖」，從而改採守勢，締結和約，維持了超過一世紀的和平。

Why is it possible for two great powers to make a transition from a long-lasting war into a time of peaceful coexistence? Structural realists believe that a balance of material capabilities can lead to peace, while constructivists remind us that we cannot ignore ideational factors. Utilizing the two-stage model from Jervis and Levy, this paper integrates both material and ideational factors and takes the Chanyuan Covenant as an example. It describes how both the Song and the Liao first obtained a material basis sufficient for self-preservation and then in the process of further expansion encountered opponents that were capable of protecting themselves. After launching more than one unsuccessful offensive, both the Liao and the Song decision-makers finally acknowledged that they had reached power parity and no longer thought that further attacks would be “profitable.” Hence, they switched to a defensive position, concluded a peace treaty, and maintained it for more than a century.