The Chanyuan Covenant of 1005 that ended decades of war between Song and Liao precipitated a new political model that, from the Song perspective, exchanged wealth, territory, and dynastic pride in return for peace along the northern frontier, civilian sovereignty over a long-dominant military class, and the replacement of a culture of arms with the love of books. That “Chanyuan Paradigm” survived the Qingli war of 1040–1044 with the Tangut Xi Xia, but was steadily overturned in the expansionist wars promoted by Shenzong and his sons from 1068 through the fall of the Northern Song in 1127. This article argues that the fragility of the Chanyuan-style peace did not stem from the aspirations of a revanchist emperor and his confidantes, but was rather the consequence of the intrinsic difficulties of maintaining peace in a world of new players, internecine political contests, and shifting geopolitical alliances that characterized the mid-eleventh century.