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The Effects of U.S. Troop Presence on Interstate Conflict

• On average, nearby U.S. troop presence is associated with a lower likelihood of interstate war.
• Nearby U.S. troop presence is associated with allies initiating fewer militarized disputes.
• These benefits appear to come with tradeoffs. Nearby U.S. troop presence is associated with a higher likelihood of low-intensity militarized disputes (e.g., displays of military force and threats to use military force).
• In addition, a large in-country U.S. troop presence is associated with potential U.S. adversaries initiating even higher-intensity militarized disputes, though still short of war.
• U.S. troop presence is associated with a higher likelihood of the United States initiating militarized disputes. This may reflect the strategic deployment of U.S. forces near states with which the United States expects to engage in military conflict.

The Effects of U.S. Military Presence on Intrastate Conflict

• The authors found no consistent or robust association between U.S. forward troop presence and intrastate conflict.
• However, overall U.S. military assistance is positively associated with an increased risk of anti-regime activities and greater levels of state repression by incumbent governments.

The Effects of U.S. Military Assistance on Conflict

• The authors found no consistent or robust association between U.S. military assistance and interstate conflict.
• However, provision of U.S. military assistance may be associated with increased state repression and incidence of civil war.

Implications for Forward Presence Decisions

• A large U.S. regional troop presence can be an effective tool in deterring interstate war, but it may also provoke more militarized activities short of war.
• With regard to U.S. efforts to deter Russia and China, the authors note that substantial nearby U.S. troop presence may in general be associated with a lower likelihood of interstate war, though it may increase the risk of provocations short of war, and these general patterns might differ in specific cases.
• U.S. military assistance, much of which has historically been in the Middle East, may overall be associated with a greater likelihood of repression or domestic instability, though the effects may differ in particular countries.

There is an ongoing debate about the effects of U.S. military presence on conflict around the globe. In one view, U.S. military presence helps to deter adversaries, restrain U.S. partners from adopting provocative policies, and make it easier for the United States to achieve its aims without the use of force. In another view, U.S. military presence tends to provoke adversaries and encourage allies to adopt more reckless policies, and it increases the likelihood that the United States will be involved in combat.

The authors of this report analyze historical data to assess how U.S. military presence — in particular, U.S. troop presence and military assistance — is associated with the interstate and intrastate conflict behavior of states and nonstate actors. Troop presence and military assistance have different effects. Stationing U.S. troops abroad may help deter interstate war. A large U.S. regional troop presence may reduce the likelihood of interstate conflict in two ways: by deterring potential U.S. adversaries from initiating interstate wars or by restraining U.S. allies from initiating militarized behavior. However, U.S. military presence may increase interstate militarized activities short of war. U.S. adversaries may be more likely to initiate militarized disputes against states with a larger U.S. in-country troop presence. U.S. troop presence does not appear to reduce the risk of intrastate conflict or affect the level of state repression. U.S. military assistance is not associated with changes in interstate conflict behavior. However, provision of U.S. military assistance may be associated with increased state repression and incidence of civil war. These findings have implications for near-term decisionmaking on U.S. forward troop presence in Europe and Asia.

• Chapter One

  Introduction

• Chapter Two

  Trends in U.S. Presence

• Chapter Three

  How U.S. Troop Presence May Influence Interstate Conflict Behavior

• Chapter Four

  Empirical Assessment of U.S. Troop Presence and Interstate Conflict Behavior

• Chapter Five

  How U.S. Presence May Influence Intrastate Conflict Behavior

• Chapter Six

  Empirical Assessment of U.S. Presence and Intrastate Conflict Behavior

• Chapter Seven

  Findings and Implications for Future U.S. Presence and Operating Environment

• Appendix A

  Interstate Model Results

• Appendix B

  Intrastate Model Results