Paul Kennedy owes a great deal to the editor who persuaded him to add a final chapter to this study of the factors that contributed to the rise and fall of European powers since the age of Spain’s Philip II. This tailpiece indulged in what was, for an historian, a most unusual activity: it looked into the future. Pondering whether the United States would ultimately suffer the same decline as every imperium that preceded it, it was this chapter that made The Rise and Fall of the Great Powers a dinner party talking point in Washington government circles. In so doing, it elevated Kennedy to the ranks of public intellectuals whose opinions were canvassed on matters of state policy.

From a strictly academic point of view, the virtues of Kennedy's work lie elsewhere, and specifically in his flair for asking the sort of productive questions that characterize a great problem-solver. Kennedy's work is an example of an increasingly rare genre – a work of comparative history that transcends the narrow confines of state– and era–specific studies to identify the common factors that underpin the successes and failures of highly disparate states.

Kennedy's prime contribution is the now-famous concept of ‘imperial overstretch,’ the idea that empires fall largely because the military commitments they acquire during the period of their rise ultimately become too much to sustain once they lose the economic competitive edge that had projected them to dominance in the first place. Earlier historians may have glimpsed this central truth, and even applied it in studies of specific polities, but it took a problem-solver of Kennedy's ability to extend the analysis convincingly across half a millennium.

保罗-肯尼迪要感谢编辑，是他说服他为这本研究西班牙腓力二世时代以来促成欧洲大国兴衰的因素的书增加了最后一章。这个结尾部分沉浸在对一个历史学家来说最不寻常的活动中：它展望了未来。思考美国最终是否会像之前的每一个帝国一样遭遇衰落，正是这一章使《大国的兴衰》成为华盛顿政府圈子里的一个晚餐聚会话题。这样一来，肯尼迪就被提升到了公共知识分子的行列，其对国家政策问题的意见被征询。

从严格的学术角度来看，肯尼迪作品的优点在于其他方面，特别是他提出那种富有成效的问题的天赋，而这些问题正是一个伟大的问题解决者的特点。肯尼迪的作品是一个越来越少见的例子--超越国家和时代研究的狭隘范围的比较历史作品，以确定支撑高度不同的国家的成功和失败的共同因素。

肯尼迪的主要贡献是现在著名的 "帝国过度扩张 "的概念，即帝国的衰落主要是因为他们在崛起期间获得的军事承诺，一旦他们失去了最初将他们推向统治地位的经济竞争优势，就会变得难以维持。早期的历史学家可能已经瞥见了这一核心真理，甚至将其应用于对特定政体的研究中，但肯尼迪这样的问题解决者才有能力将这一分析令人信服地扩展到半个世纪之久。