全球智库信息集成服务系统

General findings

• U.S. political objectives in military interventions were often successfully achieved, about 63 percent of the time, with clear failure to achieve them relatively rare, about 8 percent of the time.
• U.S. objectives have tended to become more ambitious over time, and this shift has corresponded with a gradually decreasing likelihood that objectives will be successfully achieved.

Combat and counterinsurgency interventions

• Particularly in the post-1945 era, the United States has generally been able to achieve its objectives in these interventions when it applies substantial numbers of forces, and particularly ground forces.
• The effectiveness of U.S. forces in achieving objectives in combat interventions may be augmented by the often-superior technical capabilities of the U.S. military.
• Pre-intervention planning is a key factor influencing the ability of the United States to achieve its objectives.

Stability operations

• The ability of the United States to focus on and achieve its political objectives in stability operations appears to diminish as the intensity of conflict increases.
• Nonmilitary resources and pre-intervention planning can be central to success.
• The initial quality of host-nation political institutions and the support of the host-nation government can have a substantial effect on the success of stability operations.
• Third-party interference can substantially affect the likelihood of success.

Deterrence interventions

• The United States appears to have been more successful in its pursuit of its objectives in deterrence interventions at points when the country's military capabilities vis-à-vis the rest of the world were higher, as was the case immediately after World War II.

Using an original data set of 145 ground, air, and naval interventions from 1898 through 2016, this report identifies those factors that have made U.S. military interventions more or less successful at achieving their political objectives. While these objectives were often successfully achieved, about 63 percent of the time overall, levels of success have been declining over time as the United States has pursued increasingly ambitious objectives.

The research combines statistical analysis and detailed case studies of three types of interventions — combat, stability operations, and deterrence. The research highlights that the factors that promote the successful achievement of political objectives vary by the nature of the objective and the intervention. For example, sending additional ground forces may help to defeat adversaries in combat missions but may have a more contingent effect on success in institution-building in stability operations, where nonmilitary resources and pre-intervention planning may be especially vital.

The report offers five main policy recommendations. First, planners should carefully match political objectives to strategy because factors that promote success vary substantially by objective type. Second, sending more forces does not always promote success, but for certain types of objectives and interventions, greater capabilities may be essential. Third, policymakers should have realistic expectations regarding the possibility of achieving highly ambitious objectives. Fourth, pre-intervention planning is crucial. Finally, policymakers should carefully evaluate the role that might be played by third parties, which is often underappreciated.

• Chapter One

  Introduction

• Chapter Two

  Existing Literature: Findings and Shortcomings

• Chapter Three

  Collecting Data on U.S. Military Interventions

• Chapter Four

  Factors That Affect Success: A Quantitative Look

• Chapter Five

  Factors That Affect Success: Case Studies

• Chapter Six

  Synthesis and Recommendations

• Appendix A

  Codebook: Data Collection and Definitions

• Appendix B

  Case Studies

• Appendix C

  Statistical Analyses

• Appendix D

  List of Cases