"Perhaps inevitably, fear and anger influenced U.S. policymaking in the weeks and months after the attacks. But so did other tendencies with deeper sources in Washington foreign policy establishment circles: delusions of grandeur, threat inflation, faith in the ability of armed force to solve political problems, and a refusal to accept limits and trade-offs. As President George W. Bush’s fatefully termed “Global War on Terror” enters its third decade, its enormous costs proliferate.

The price tag is staggering. More than 7,000 American military personnel have died in the U.S.-led wars worldwide since 9/11, and as of 2015, another 50,000-plus had been wounded. An additional 30,000 active-duty personnel and veterans of these wars have died by suicide. More than 7,402 U.S. contractors were also killed, in Afghanistan and Iraq alone. The direct deaths in the wars were upward of 800,000, but Brown University’s Costs of War project, which supplied the data in this paragraph, found that several times that were killed indirectly through such causes as war-related disease and water shortages. As of last year, the wars have cost about $6.4 trillion, and there will be the future costs of service members’ long-lasting benefits. And finally, the wars have created at least 37 million refugees.

In addition, civil liberties have been curtailed, innocent Muslims have been entrapped and targeted, and the constant drumbeat about defeating Islamists abroad has fueled rampant Islamophobia and white nationalism at home. “The anti-Muslim discourse that arose in the wake of 9/11 was a vector through which open racism and open bigotry was smuggled back into the mainstream of American politics,” said Matt Duss, Bernie Sanders’s foreign policy adviser. Broad, hateful generalizations about Muslims and Islam became permissible because of the trauma of the attacks. “I think it normalized these sorts of claims about different groups of people, immigrants, Latinos, Asians, Black people, or others,” Duss said. Donald Trump exploited that bigotry in his 2016 election campaign.
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Lessons from the 9/11 Era

In environments like this, modest, prudent, long-term strategy is indispensable. So are prioritizing vital interests, reducing unnecessary conflict, and husbanding resources. Alas, the story of U.S. foreign policy since 9/11 is largely a story of squandering human lives and wealth, recklessly damaging the country’s valuable capabilities and soft power. America’s supreme position in the 1990s meant that it had a huge cushion of power to squander through failed military interventions, trillion-dollar wars, and wasteful defense spending. But that cushion has shrunk. Al Qaeda failed in ejecting the United States from the Middle East—the nation still supports repressive governments in Saudi Arabia, Egypt, Israel, and elsewhere. But the 9/11 attacks were wildly successful in pushing the United States to engage in profoundly destructive acts that damaged U.S. security, to say nothing of the lives lost elsewhere.

In small ways, because of the consistent string of failures, Washington has become friendlier to the idea of a foreign policy oriented around restraint or retrenchment. The Quincy Institute for Responsible Statecraft, a think tank founded in 2019, is a vital counterweight in offering the media and lawmakers policy-relevant research from a perspective that sees U.S. power and interests as limited and selective rather than inexhaustible and global. “Restraint is now part of the conversation,” said Andrew Bacevich, the institute’s president. “But I don’t think something like any kind of a deal has been closed.”

There does appear to be at least a temporary injunction in Washington on trying to build states abroad. As Khanna said, the country is now “more cautious about the ability of military interventions to transform societies. Do I think that there could be overreaction still on civil liberties and certain misguided forays of foreign policy? Of course, but I do think that we’ve learned the lesson of Iraq.”

But it’s not clear that members of the foreign policy establishment believe their track record is spotty. “If you do the balance of where we are today and what we’ve done after 20 years, the war on terror certainly has been a lot costlier than we wanted, with very imperfect results in the region, for the quality of life and governance in the Middle East—but it’s actually still been somewhat successful,” said Michael O’Hanlon. Kenneth Pollack noted that, while the Iraq War was horribly mismanaged and the United States made other mistakes, “back in 2001, nobody believed that, over the next 20 years, there wouldn’t be another major terrorist attack.”

These accounts suggest that Al Qaeda’s inability to replicate its attacks means that U.S. strategy has been effective and wise. That assessment underestimates the scale and frequency of foreseeable U.S. failures in favor of praising an outcome that would have been easier to attain without spending trillions of dollars and causing the deaths of hundreds of thousands.. It’s like a person needing a car worth $25,000 who spends $1 million on the car at a dealership, has a few drinks while driving it home, receives a few speeding tickets, and causes a hit-and-run that kills somebody—but who declares success because he did, in fact, get the car.

What’s more, policymakers in both parties and some foreign policy intellectuals overlook maybe the key lesson of the past 20 years, which is that the use of armed force often weakens America’s international position. Democrats and Republicans alike worry that reduced U.S. influence globally would be replaced by China, Russia, Iran, or other nefarious actors.. But this assumes that the United States is endangered whenever other countries exercise power. “Foreign policy should be about interests, not vacuums,” Barry Posen said. “If your interests don’t lie in a place, why do you care?”

The country could use its power advantageously. Few things would benefit the United States more than converting enemies and challengers through tough-minded diplomacy rather than perpetually trying to coerce them with sanctions, bombastic rhetoric, or armed force. The Iran deal, Russia’s commitment to America’s terrorism project from 2001 to 2003, and China’s continual ideological shifts throughout the decades suggest that skillful, creative diplomacy and due recognition of the interests of other countries can reduce tensions, offer opportunities for cooperation, and prevent the emergence of coalitions that balance against the United States. “Trying to befriend adversaries is an important tool of statecraft that often gets overlooked,” said Charles Kupchan, author of How Enemies Become Friends: The Sources of Stable Peace.

Domestic challenges and intense political polarization make robust diplomacy and peacemaking difficult, however, not just with the Taliban circa 2002 but perpetually. “There’s always a nationalist waiting in the wings to say you’re selling out the country, you’re being weak in the face of danger,” Kupchan said. Forefronting diplomacy also would mean acknowledging other countries’ interests, dealing directly with adversaries, and accepting imperfect agreements. Because the best way to secure the United States is to preserve its power, narrow its list of vital interests, and build a better country at home, not squander blood, treasure, and soft power in the futile pursuit of global dominance and armed humanitarianism. That is a view that hasn’t gained prominence in Washington. It certainly didn’t after 9/11. Perhaps one day it will.

For better and worse, the foreign policy establishment is weaker and more fragmented than it has been since the end of the Vietnam War. But it still exists, and it has tentatively learned some things from the wasteful, counterproductive, and sometimes disastrous U.S. foreign policy performance of the last 20 years. “The real problem with Afghanistan was the decision to try to occupy the country, and to try to eradicate the Taliban, and transform it,” said Kenneth Pollack. “I think that we’ve learned that that was ultimately impossible.”

But even the withdrawal from Afghanistan is highly controversial among some of the elite. And the demonization of other countries and peoples, the inability to understand the worldview of challengers and adversaries, the overreliance on force: these traits remain, because they were ingrained in Washington long before 9/11. Because of its unchallenged international position, the United States was able to make major mistakes for two decades after the Twin Towers fell and still emerge predominant. However, with an emerging China possessing nuclear weapons, a growing economy, the world’s biggest population, and expanding demands, the United States cannot afford another 20 years of failure.
https://newrepublic.com/article/163119/twenty-year-anniversary-911-attacks

The article is kind of long. It is a summary of US policies before and after 9/11. The quoted text above only includes opening and the closing paragraphs.