It has been a decade since 19 Islamic terrorists hijacked airplanes and flew them into U.S. landmarks. That savage attack marked the beginning of a new era in modern history. The decade has been marked by war, and the deepening of cleavages inside and between almost every country on the planet.

As the dust cleared on that day, the world witnessed many incidents of heroism and the best that humanity has to offer. Since then, though, much of the very worst has been on display as well. The easiest way to measure the impact of Sept. 11, 2001, is to tote up the costs, and they are staggering.

“The Costs of War,” by Brown University’s Watson Institute for International Studies, calculates the final cost of the wars waged and led by the United States as between $3.7 trillion and $4.4 trillion. That includes the cost of fighting the wars themselves, the long-term obligations to veterans and paying debts incurred because the U.S. chose deficit financing rather than taxes to pay for the wars.

These costs apply just to the United States — no one else seems to have had the stomach to calculate the economic damage done to them.

The price tag in economic damage from the 9/11 attacks is reckoned to be between $50 billion and $100 billion. Neither that estimate, nor the one from “The Costs of War,” includes costs generated by new security measures such as airport security, supply chain safety, or the unknowable price paid by closing borders to travelers.

How can any country calculate the loss of brainpower and creative energy that has resulted from the new difficulties attendant to getting a visa, for example?

Nor do those numbers include the lives lost. More than 3,000 people from over 50 countries died on 9/11. Since then, 224,000 to 258,000 people have died from related warfare, including 125,000 civilians in Iraq.

Countless thousands of other lives have been lost as a result of the indirect effects of war — loss of clean drinking water, health care, and nutrition. An additional 365,000 have been wounded and 7.8 million people displaced.

Staggering though these costs are, they are probably not the most significant. Americans rue the damage that has been done to U.S. power and prestige.

For all its bluster — remember President George W. Bush’s famous warning that countries were “either for us or for the terrorists”? — the world’s sole remaining superpower has emerged a decade later weakened, more from its own actions than as a result of anything done to it.

Resorting to such measures as “rendition” and torture, while insisting that its actions are beyond the purview of international law, has undermined the authority and credibility of the U.S. We say this as an ally and friend of the U.S.

Sadly, this trend is global. Far too many governments have turned a blind eye to — or worse, actively pursued — the erosion of personal freedoms in the name of greater security.

As one sad measure of this phenomenon, a recent study estimates that at least 35,000 people worldwide have been convicted as terrorists since 9/11 and that 120,000 have been arrested as terrorists.

The real crime of many of these individuals is merely protesting or opposing their governments.

This may be the most pernicious effect of 9/11 — the culture of fear, mistrust and suspicion that now dominates the world. In an age of globalization and interdependence, diversity is inevitable and indeed may be essential to success.

Tolerance should be promoted; instead, dividing lines among countries and civilizations have been sharpened.

One of the deepest divides is between Muslims and the West. Islam has no monopoly on extremism, but in the aftermath of 9/11, a hostility erupted that has disrupted relations between them to this day. This emotion colors the analysis and assessment of every event in the Middle East, Africa, and even parts of Southeast Asia.

It is the filter through which we have viewed the Arab Spring, elections in Indonesia and Malaysia, the struggle between Israelis and Palestinians, to name just a few. Natural support for democracy is constrained by concern of what “the Street” might do if unrestrained.

What may be worst of all is the sense of isolation that has sprouted throughout the world.

Blame the sense of helplessness, which is a byproduct of terrorism. Terrorists hope to instill the fear that risks cannot be controlled, that life is uncertain and that not even governments can protect us. Byproducts of this fear are mistrust in anyone who looks different — even neighbors — and erosion of the social contract. After all, safety is the cornerstone of society.

A few years after 9/11, a former U.S. government official noted ruefully that, in the aftermath of that day, the U.S. let fear, rather than hope, dominate its response.

The results of that decision are evident today in the rise of protest movements that insist that their governments do not understand them — whether it is the Arab Spring in northern Africa, the tea party in the U.S. or the hooligans that lit up British cities this summer.

Their anger stems from a lack of faith in their institutions, an existential crisis that swells in tandem with the economic issues that come from the fraying of social bonds. We cannot blame all of this on the U.S. response to 9/11, but the blame begins here.

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