LAUSR

ABSTRACT Private military and security companies are integral components of the defense and intelligence operations of some of the world's most powerful states. Despite the increasingly pivotal role of contractors, analysts have yet to develop theories explaining when governments should outsource national security responsibilities or what conditions cause private defense markets to function efficiently. This inquiry addresses this gap in the literature by demonstrating that varying market structures—that is, the quantity of firms providing similar services and the number and purchasing power of those buying these services—have significant effects on costs, oversight, and company performance in the private defense industry. A principal–agent framework is developed to explain variation in the performance of firms in different markets across the industry. Evaluation of three private defense markets yields the surprising conclusion that monopsony, rather than a competitive market, is the ideal structure for governments outsourcing aspects of national defense.