Students of international relations have long argued that large and rapid shifts in relative power can lead to war. But then why does the rising state not alleviate the concerns of the declining one by reducing its expected future power, so that a commitment problem never emerges? For example, states often limit their ability to launch preemptive attacks by creating demilitarized zones, or they abandon armament programs to avoid preventive wars. In a model of complete information, I show that shifts in power never lead to war when countries can negotiate over the determinants of their power. If war occurs, then, it must be that negotiations over power are impossible or too costly. I then show how third parties, domestic politics, and problems of fungibility can increase the costs of such negotiations, and hence lead to war, even under complete information.Keywords: conflict; causes of war; bargaining; power; war; power shifts Students of international relations have long argued that rapid shifts in relative power can lead to war. 'The growth of Athenian power and the fear which this caused in Sparta' or the rise of Germany, for example, are common explanations for the Peloponnesian war and World War I, respectively.1 More recently, the economic and military rise of China has led many to wonder about the likelihood of a war with its neighbors or the United States. 2 In each case, the declining state fears that it will negotiate in a position of weakness once the balance of power has shifted, 1 The quote is from Thucydides (1984). The rise of Germany as a cause for World War I is discussed in Joll (1992), and with a twist, in Ferguson (1999, 83): 'The key to the arms race before 1914 is that one side lost it, or believed that it was losing it. It was this belief which persuaded its leaders to gamble on war before they fell too far behind'. See also Ferguson (2006). 2 See, for example, Hoge (2004), Bijian (2005), or Mearsheimer (2006.
228terms of use, available at https:/www.cambridge.org/core/terms. https://doi.org/10.1017/S175297191100008XDownloaded from https:/www.cambridge.org/core. University of Basel Library, on 11 Jul 2017 at 17:31:41, subject to the Cambridge Core and hence it is argued, prefers fighting now. The problem is not that there are no peaceful solutions that both parties would prefer to war; the costs and risks of war ensure that there always exists such an agreement. 3 Rather, fighting occurs because any commitment to a specific course of action once the balance of power has shifted is inherently non-credible. This line of argument, however, is problematic. If indeed rapid changes in relative power lead to inefficient conflicts, then why do states not negotiate over the causes and speed of this shift. In other words, why would the rising state not offer today concessions of capabilities that reduce his expected power tomorrow? Abandoning a weapons program or withdrawing troops from the border, for example, are simple ways to alter expected incentives in the next period, and hence to credi...