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.

Our findings flip the conventional wisdom on its head: irrespective of whether the United States intervened, the outcomes were largely the same. Across each of the dimensions we considered, there was no statistically significant difference between the cases that prompted an intervention and those that did not. In other words, the evidence that U.S. military interventions are consistently achieving their goals is sparse. But this does not mean that all interventions fail. A closer look suggests that there is a subset of operations that is more likely to advance U.S. interests and achieve U.S. objectives: those that had clear, achievable goals and were informed by accurate assessments of local conditions.

Washington desperately needs to rethink its relationship to military force. Above all, it needs to stop regarding military adventures as the go-to solution for all potential threats. At the same time, however, it cannot view every potential intervention as an inevitable disaster that will divert resources from domestic priorities. The real danger is not military interventions per se but large ones with expansive objectives that are out of touch with the reality on the ground. Those are the ones that gamble with U.S. blood and treasure.

Although there is strong evidence that setting such expansive goals often leads to failure, our analysis shows that the decision to use military intervention to accomplish broad objectives has become increasingly common since World War II. Before the war, the United States intervened primarily to conquer other lands or defend its own. But after, when the Cold War began, American ambitions grew. Washington now sought to enhance regional security, oppose communism, rebuild countries, and promote global norms. After the Cold War, counterterrorism was added to the list of goals, and although the United States did not intervene more frequently, its aims steadily became more wide-ranging. Not surprisingly, heightened ambitions lowered the success rate of American interventions, and despite having the most powerful military on the planet, the United States often met with failure. Since the early 1990s, then, the share of interventions that failed to achieve their objectives has risen steadily. Our analysis suggests that before 1945, the United States achieved about 80 percent of its intervention objectives. During the Cold War, however, it achieved its objectives only about 60 percent of the time, and in the post–Cold War period, the rate of success has fallen to just under 50 percent.

Critics might argue that our study has a selection problem, if the crises and conflicts in which the United States intervened were also the ones that were most likely to fail no matter what. But there is little evidence to support that objection. Dozens of case studies suggest that there is no relationship between the difficulty of the underlying circumstances and the likelihood of intervention: there are plenty of hard cases in which the United States intervened and plenty of easy cases in which it chose not to. But as constraints on U.S. military power faded during and after the Cold War, the United States did adopt more and more expansive goals for the interventions it chose to pursue and was consequently less and less able to achieve these goals by relying solely on military force.