Several weeks ago the Defense Department revealed it is seriously considering drone strikes against Islamist terrorists in the Philippines, which would make it the eighth country the United States has bombed in the war on terror. Certainly the terrorists—who have operated in various forms there for over a hundred years—are a threat to Filipinos. They are not, however, a threat to the United States. Why, then, would the United States start bombing?

The answer may lie in the misguided theory driving American thinking about terrorism.

During the Cold War, America’s political leaders subscribed to the domino theory. The theory, whose name comes from a 1954 speech by President Eisenhower, held that if one country fell to communism, then its neighbors would fall next, toppling like dominoes. This fear encouraged U.S. officials to worry about the emergence of communism even in places of little strategic importance.

History reveals that the domino theory was a poor guide to international relations, but its power during the Cold War was real. The United States intervened repeatedly in the Third World, toppling governments and fueling civil conflicts, in order to prevent the spread of communism. Most importantly, the domino theory provided the primary justification for the Vietnam War, which cost the United States almost 60,000 lives and also strained the fabric of American society. Tragically, the irrelevance of the loss of the Vietnam War for American security was not enough to vanquish the domino theory. It continued to motivate American intervention in Central America and elsewhere until the collapse of the Soviet Union.

The 9/11 attacks in turn spawned what we might call the pandemic theory. According to this theory, terrorism spreads as the terrorism “contagion” jumps from person to person, oblivious to distance or national borders. Thanks to its viral spread, which can occur via interpersonal contact or online through propaganda and chat rooms, terrorism anywhere in the world is a threat to reach the U.S eventually. As with infectious diseases, even a small outbreak of terrorism in a faraway land can be used to justify extreme responses. The best time to eradicate a disease, after all, is before it gets a foothold and infects a large number of people.

The pandemic theory looks compelling at first glance. But like many popular theories, it is dangerously inaccurate.

First, terrorists themselves do not suffer from a disease. Instead, they almost always have a specific political goal, and their choice of violence to achieve that goal typically derives from a coherent thought process. Scholars have shown that even seemingly unthinkable acts like suicide bombing follow a strategic logic, with their horrific nature making such acts particularly potent tools for generating fear and attention. The bombers themselves are a mix of the willing and angry and those forced into it, including the young and mentally disabled. But suicide terrorism occurs not because terrorists are sick, but because terrorist organizations believe it is a useful coercive weapon.

Second, terrorism does not spread like an infectious disease. Ideas animating the group may have appeal (e.g., esprit de corps and income for unemployed males, promises of power for the disenfranchised). However, terrorism’s spread is limited to those who are willing to kill their fellow human beings. Thankfully, there are very few of those people. Indeed, the act is so unnatural that militaries have difficulty training recruits to kill. Evidence shows that even in combat, soldiers will often fail to kill unless they have been repeatedly conditioned to do it. It is no wonder, then, that most terrorist groups eventually decide to enter the political process or wind up marginalized after failing to reach their objectives.

Third, unlike a pandemic, terrorism’s deadly impact is geographically limited. The historical evidence shows that the vast majority of attacks occur in war zones or failed states. Just one country—Iraq—endured nearly a quarter of all terror attacks over the past 16 years, while ten countries account for 73 percent of the total. All ten of the countries experienced a war during that time. Conversely, stable and developed countries rarely experience terror attacks. The United States and nine peers (e.g., Canada and the UK) only experienced two percent of the attacks.

What makes the pandemic theory so attractive, then? The psychological shock and fear induced by 9/11 probably has something to do with it. It is also true that some terrorist groups, like Al Qaeda and ISIS, have managed to spread, at least to some degree.

But a clear‐​eyed assessment shows that the Islamist “virus” is severely self‐​limiting. Though Al Qaeda and the Islamic State have shown some capacity to inspire lone wolf attacks against America and other nations, those attacks are relatively few in number. Moreover, there is no sign that their ideology has taken root within the United States (or anywhere else) despite massive levels of terrorism in the Middle East and their purported mastery of digital propaganda.

In short, though terrorism is a terrible scourge and sometimes a threat to the United States, it does not behave like a pandemic. Terrorism elsewhere, whether in the Middle East, Latin America, or the Philippines, is not automatically a threat to America.

Unfortunately, bad theories lead to bad policy. Just as the domino theory led to tragic and unnecessary wars to contain communism, pandemic theory has led the United States to wage a costly and fruitless war on terrorism. As long as pandemic theory dominates official thinking, there is no end to the war in sight.