The issue of “preemptive” war is more in the news now than at any time since the invasion of Iraq in 2003. The impetus, of course, is the rapid development of North Korea’s nuclear and missile programs, which will soon give Pyongyang the capability to hit any American city with a nuclear-tipped ICBM. President Trump has been threatening “fire and fury” in response, and warning that the United States is “locked and loaded” for war. His national security adviser, Lt. Gen. H.R. McMaster, has said that North Korea may not be deterrable and that, therefore, a preemptive strike may be justified.

In truth, the use of “preemptive” in this context is a misnomer. In international law, a “preemptive” strike is one undertaken just before an enemy attack. There are few examples of such conflicts beyond the 1967 Six Day War. The use of force in such an instance is labeled “anticipatory self-defense” and is clearly legal and logical. If Washington were to acquire intelligence that North Korea was about to attack the United States—or even U.S. allies such as South Korea and Japan—there is no doubt that a preemptive strike would be warranted.

But that is not the situation the U.S. faces at the moment. If it were to attack North Korea today, it would be launching a preventive, rather than a preemptive, war—a war intended to address a future, rather than imminent, threat. The strategic and legal rationale for such a move is far shakier. There are a few instances where preventive strikes were undoubtedly wise—e.g., Israel’s attacks on nuclear facilities in Iraq (1981) and Syria (2007)—even if not strictly sanctioned under international law. There are also widely cited examples of when a preventive war would have made sense—for example, against the growing power of Nazi Germany in the 1930s. (It may, however, be argued that such a conflict would not have been truly preventive because it would have occurred after Hitler had already provided a casus belli by violating the Treaty of Versailles.)

But history is also littered with preventive wars that are widely considered a mistake and sometimes a crime. These include the German attack on France and Belgium in 1914 (motivated by fear of rising Russian power—in order to strike at Russia the German General Staff decided to first defeat Russia’s ally, France); the German attack on the Soviet Union in 1941 (motivated, again, by fear of its rising power); the Israeli attack on the Sinai in 1956 (designed to avert an Egyptian threat, it led to a humiliating climb-down by Israel in the face of American pressure); and of course the U.S. invasion of Iraq in 2003, which was based on a faulty premise (Iraq’s WMD program was not nearly as far advanced as U.S. intelligence feared) and plagued by faulty execution. ...