Increased counterterrorism measures simply transfer terrorists' attention elsewhere. Installing metal detectors in airports in 1973 decreased skyjackings but increased kidnappings; fortifying American embassies reduced the number of attacks on embassies but increased the number of assassinations of diplomats. Since counterterrorism measures were increased in Europe, the United States and Canada, there has been a clear shift in attacks against US interests to the Middle East and Asia.

Spending ever-more money making targets "harder" is actually a poor choice. Increasing defensive measur...

Increased counterterrorism measures simply transfer terrorists' attention elsewhere. Installing metal detectors in airports in 1973 decreased skyjackings but increased kidnappings; fortifying American embassies reduced the number of attacks on embassies but increased the number of assassinations of diplomats. Since counterterrorism measures were increased in Europe, the United States and Canada, there has been a clear shift in attacks against US interests to the Middle East and Asia.

Spending ever-more money making targets "harder" is actually a poor choice. Increasing defensive measures worldwide by 25% would cost at least $75 billion over five years. Terrorists will inevitably shift to softer targets. In the extremely unlikely scenario that attacks dropped by 25%, the world would save about $22 billion. Even then, the costs are three times higher than the benefits.

Put another way, each extra dollar spent increasing defensive measures will achieve - at most - about 30 cents of return. We could save about 105 lives a year in this best-case scenario. To put this into context, 30,000 lives are lost annually on US highways.