Title: Credibility is Not Enough
Description: The United States commands the most powerful conventional military in the world. This extraordinary advantage in conventional power should enable the United States to coerce target states without having to fire a single shot. Yet, over the past two decades, leaders of Iraq, Haiti, Serbia, Afghanistan, and Libya have dismissed U.S. threats and invited military clashes with the world's sole superpower. What explains the United States' inability to coerce many of the world's weakest targets with compellent military threats? I argue that the United States' compellent threats fail more frequently in the post-Cold War period because they are costly neither to issue nor to execute. That is, because it is not risky for the United States to issue compellent threats, and because it is relatively cheap for the United States to use military force, the threat of force does not signal to target states that the United States is highly motivated to defeat them. For this reason, a target will resist a U.S. threat that is immediately credible in the belief that the United States will apply limited force, but will not apply decisive force if the target continues to resist after the United States executes its threat.

The costly compellence theory asserts that only threats that are costly for the unipole to issue and to execute will be effective in compelling target states to yield before the application of force. To illustrate this logic, I present a basic formal model of a unipole that issues a compellent threat against a weak target state. The model suggests that both unipoles that are highly motivated to prevail over targets and those that are not will behave identically in the early stages of a crisis, i.e., they are both willing to execute military threats in many equilibria. The model suggests that, under many conditions, the target cannot infer from the willingness to issue and to execute a compellent threat that the United States is highly motivated to defeat it, and consequently, it is likely to resist. I then argue that the United States has developed a model of warfare that dramatically limits the human, political, and financial costs of employing force. As the unipole, it is not costly for the United States to issue compellent threats in the post-Cold War period.

The United States has also pursued many strategies that limit the costs of force: it relies on an all-volunteer military increasingly supplemented by private contractors; it has developed a force structure based on the Revolution in Military Affairs (RMA) thesis that relies increasingly on airpower and unmanned aerial vehicles (UAVs); it employs force in conjunction with allies who contribute money and troops to U.S. coercive campaigns; it employs deficit spending to pay for its military operations; and, it actively limits collateral damage inflicted on target states. In combination, these strategies both lower the costs of employing force and undermine the effectiveness of U.S. compellent threats. To evaluate the logic of the costly compellence theory, I present a new dataset on the United States' use of compellent threats 1945-2007. I demonstrate that the United States has employed compellent threats more frequently since the end of the Cold War, and that these threats have been less effective on average in the post-Cold War period.

These observations are consistent with the logic of the costly compellence theory. I also evaluate four cases in which the United States issued compellent threats against weak opponents. The 1962 Cuban Missile Crisis and the 2011 threat against Libya constitute "most-likely" cases for the costly compellence theory. The theory accurately predicts that the Soviets would concede in 1962 and that Qaddafi would resist the United States' demands in 2011. I also compare the United States' 1991 and 2003 threats against Saddam Hussein. Saddam's resistance in 1991 is consistent with the logic of costly compellence. I evaluate sources captured after the 2003 invasion of Iraq to evaluate why Saddam Hussein chose to resist the more costly threat in 2003. Finally, I argue that the United States is likely to continue its efforts to minimize the costs of employing force and to emphasize the use of technology over ground troops. My study suggests that these strategies will both enhance the ease with which the United States can employ force and decrease the effectiveness of U.S. compellent threats, because they suggest to potential targets that the United States lacks the motivation to defeat them.