American soldiers have been deployed abroad almost continuously since the end of World War II. The best-known foreign interventions—in Vietnam, Afghanistan, and Iraq—were large, long, and costly. But there have been dozens of other such deployments, many smaller or shorter, for purposes ranging from deterrence to training. Taken as a whole, these operations have had a decidedly mixed record. Some, such as Operation Desert Storm in 1991, which swept the Iraqi dictator Saddam Hussein’s forces out of Kuwait, largely succeeded. But others—such as those in Somalia, Haiti, Afghanistan, Iraq, Libya, and elsewhere—were disappointments or outright failures. It is these unsuccessful post–Cold War interventions that have engendered serious doubts among policymakers and the public about the role of force in U.S. foreign policy.
Even so, U.S. decision-making still has a strong bias in favor of military intervention. When crises emerge, the pressure for a U.S. military response is often immediate, on the grounds that it is better to try to control the situation than to do nothing. But in many cases, the United States could likely have achieved its goals without intervening militarily. To explore how often U.S. military interventions have advanced U.S. objectives, we built a database of conflicts and crises that involved U.S. interests between 1946 and 2018. Conflict cases were drawn from the Uppsala Conflict Data Project and crisis cases came from the International Crisis Behavior data set. To identify cases involving U.S. interests, we looked for conflicts and crises that posed a direct threat to the U.S. homeland or to a U.S. treaty ally, occurred in a region of high strategic importance for the United States, or involved a large-scale humanitarian crisis. We then identified those conflicts and crises that prompted the deployment of U.S. military forces. To be counted as an intervention, the U.S. forces had to meet certain thresholds (at least 100 personnel for a full year, or a larger presence for a shorter time in the case of ground interventions). For each conflict or crisis, we also collected information on several outcome measures including conflict or crisis duration, intensity, changes in economic development and democratic institutions in the country affected by the conflict or crisis. Of the 222 conflicts and crises from 1946 to 2018 that involved U.S. interests, the United States chose to intervene on 50 occasions and not to intervene on 172.
