The cost of the global war on terror since the attacks of 9/11? Almost $4 trillion.

That’s almost half of what the U.S. has added in debt since 2001:

Without the war on terror, America’s national balance sheet would look much healthier.

So has it been worth it?

America’s free spending national security hawks, frothy at the mouth, might say yes.

But the deeper reality seems to be that terrorism is a relatively small — and some would say negligible — threat:

The chronic exaggeration of U.S. national security threats also extends to the security of individual Americans. Since 9/11, a total of 238 American citizens have died from terrorist attacks, or an average of 29 per year. To put that in some perspective, according to the Consumer Product Safety Commission, the average American is as likely to be crushed to death by televisions or furniture as they are to be killed by a terrorist. A recent study from Duke University found that, since 9/11, eleven Muslim Americans were involved in active terrorist plots in the United States, which killed thirty-three Americans. Over that same time period, there have been nearly 150,000 murders and over 300,000 suicides.

So should we declare war on people being crushed to death by televisions and furniture?

Most tellingly, from 1980 to 2005 only 6% of all terrorist events in the U.S. was Islamist in nature:

The spectacular imagery of 9/11 blinded American policymakers. Whether it was a case of guilt as a result of their failure in spite of the warnings to protect America, or whether it was that the events of 9/11 became an excuse to exercise preconceived (and in my view ill-conceived) foreign policy objectives, policymakers matched the spectacular image of 9/11 with an equally spectacular spending spree.

And yes — America has not been hit by a spectacular terrorist attack since. But it hadn’t really been hit by a spectacular terrorist attack before. 9/11 was  — whatever your wider view of the incident — a black swan event: high impact, and unprecedented. And the problem with black swan events is that very often they are not repeated, and so spending money to prevent future occurrences is more or less a waste of money.

America faces a whole swathe of real risks far far bigger than international terrorism including derivatives contagion, global trade fragility, climate instability, and electromagnetic pulses. We don’t know what the next calamitous black swan event will be. But I’m pretty sure that a whole boatload of money will be spent on preventing it after it has happened, just as trillions have been wasted on preventing jihadist terrorism after it has already done the damage.

And the biggest problem here is the spending. $4 trillion of productivity was wasted. Keynesian multipliers are irrelevant — the money would surely otherwise have still been spent, and on more productive and useful endeavours. That’s a pretty big opportunity cost.