Patricia L. Sullivan

Finds that the nature of the belligerents’ war aims determines whether military strength or tolerance for costs will be the most important determinant of a war’s outcome. Militarily strong states almost always succeed when they engage their ground forces in direct attempts to seize territory or overthrow foreign regimes, but the weak become more likely to prevail when their strong adversaries have less tangible political objectives.

Demonstrates that, with limited exceptions, increasing U.S. military aid significantly reduces other countries’ level of foreign policy cooperation with the United States. U.S. reaction to recipient state behavior is also counter-intuitive: our results show that recipient state cooperation is likely to lead to subsequent reductions in U.S. military assistance.

Shows that the effect of public approval on the duration of military operations initiated by powerful democratic countries varies based on which party is in power. As public support for the chief executive declines, governments on the right of the political spectrum are inclined to continue to fight, while left-leaning executives become more likely to bring the troops home.

Shows that where there is uncertainty about the human and material costs of attaining a country’s war aims, strong states are at increased risk of entering long, costly, and ultimately unsuccessful military engagements. Military interventions by major powers with objectives that can be attained with “brute force” last an average of 15 months, and 75% are successful. When strong states use military force in an attempt to attain objectives that are dependent on target country compliance, their military interventions last an average of 36 months and the main political objective is eventually attained in less than 50% of cases.

Demonstrates that concern about the costs of withdrawing from a conflict can be a more important determinant of the public’s willingness to persevere than concern for the costs of fighting the war. Pre-war, individuals are more likely to support the use of force when the military intervention would not involve ground troops and when it would be undertaken with the support of allies. Once an actual military intervention has been initiated, the public is significantly more likely to support sustaining the operation if it is unilateral and more than ten thousand ground troops have been deployed.

Finds that despite overwhelming military superiority, major powers frequently fail to attain their objectives when they use military force abroad because they choose to terminate military operations when they decide that the cost of victory will exceed the price they are willing to pay to secure those objectives. Since World War II, in all military interventions by major powers, the latter prevail more often than their weak state and nonstate adversaries. But weak actors thwart the objectives of their powerful opponents almost two-thirds of the time when the major powers pursue war aims that are dependent on attaining the weak state’s compliance.