WASHINGTON — Twenty years ago, when the twin towers and the Pentagon were still smoldering, there was a sense among America's warrior and diplomatic class that history was starting anew for the people of Afghanistan and much of the Muslim world.

"Every nation has a choice to make," President George W. Bush saidon the day that bombs began falling on Oct. 7, 2001. In private, senior U.S. diplomats were even more explicit. "For you and us, history starts today," then-Deputy Secretary of State Dick Armitage told his Pakistani counterparts.

Earlier this month, as the Taliban raced across Afghanistan, retired Lt. Col. Jason Dempsey, a two-time veteran of the war, stumbled across Armitage's words. To Dempsey, the sentiment was "the most American thing I've ever heard" and emblematic of the hubris and ignorance that he and so many others brought to the losing war.

"We assumed the rest of the world saw us as we saw ourselves," he said. "And we believed that we could shape the world in our image using our guns and our money." Both assumptions ignored Afghan culture, politics and history. Both, he said, were tragically wrong.

The near-collapse of the Afghan army in the space of just a few stunning weeks is prompting the military and Washington's policymakers to reflect on their failures over the course of nearly two decades. To many, the roots of the disaster go back to the war's earliest days, when the Taliban were first driven from power and the United States, still reeling from the shock of the 9/11 attacks, set about building a government in Kabul.

Some two dozen prominent Afghans met in Bonn, Germany, with officials from the U.S. government, NATO and the United Nations to form a new Afghan government crafted in the image of the United States and its European allies.

"You look at the Afghan constitution that was created in Bonn and it was trying to create a Western democracy," said Michèle Flournoy, one of the architects of President Barack Obama's troop surge in Afghanistan in 2010. "In retrospect, the United States and its allies got it really wrong from the very beginning. The bar was set based on our democratic ideals, not on what was sustainable or workable in an Afghan context."

Flournoy acknowledged in hindsight that the mistake was compounded across Republican and Democratic administrations, which continued with almost equal fervor to pursue goals that ran counter to decades - if not centuries - of the Afghan experience.

By 2009, when Obama took office, it was clear to just about everyone that the United States was losing the war.

To reverse Taliban momentum and give U.S. officials a chance to build up the Afghan government and security forces, Obama signed off on a surge of troops that more than doubled the size of the American force in Afghanistan.

Flournoy said she was initially hopeful that the plan could work. On trips to Afghanistan, she met frequently with young Afghans, including women's groups, who shared America's vision for the country. They wanted to send their daughters to school, serve in government, start businesses and nonprofits. They wanted women to be full participants in society and craved a predictable political and legal system. "We found all kinds of allies," she said.

But those individuals were no match for the rot that had permeated the Afghan government. She and other U.S. officials understood that with all the U.S. money floating around in Afghanistan, there would be "petty corruption," she said. What U.S. officials discovered in 2010, after the surge was already underway, was a corruption that ran far deeper than they had previously understood and that jeopardized their strategy, which depended on building the legitimacy of the Afghan government.

"We realized that this is not going to work," Flournoy said. "We had made a big bet only to learn that our local partner was rotten."

Now, as Taliban fighters race toward Kabul and the Afghan military crumbles, Flournoy said her thoughts often turn to the Americans who sacrificed for the mission and to those "wonderful allies" who shared the U.S. hopes for a democratic Afghanistan. "That's what makes me so sick to my stomach," she said. "We invested in this whole generation that is about to suffer through this very horrible chapter."

Meanwhile, current and former U.S. officials are trying to make sense of why a government and security forces built over two decades at a cost of more than $100 billion dollars are collapsing so quickly.

Carter Malkasian, a longtime adviser to U.S. commanders in Afghanistan, has pegged the weakness of the Afghan forces on their lack of a unifying cause that resonates with Afghans, as well as their heavy dependence on the United States. By contrast, the Taliban were fighting for their culture and Islam. They "exemplified something that inspired, something that made them powerful in battle, something closely tied to what it meant to be an Afghan," Malkasian writes in his new book, "The American War in Afghanistan."

It's an observation that speaks to the limits of American power and raises the broader question of how the catastrophic and embarrassing failure in Afghanistan might constrain U.S. foreign policy moving forward.

"We know what happens when we fall to imperial hubris. What does one do with imperial heartbreak?" asked John Gans, who served as a civilian in the Pentagon during the Obama administration.

So many of today's rising military commanders and foreign policy experts were drawn into government service by the 9/11 attacks and the war in Afghanistan. After the relatively low-stakes peacekeeping missions of the 1990s, America and U.S. foreign policy suddenly seemed to be at the center of the world in the years after 2001. A whole generation of leaders driven "by ambition, ego and a desire to shape world events" ran toward the action, Gans said.

Their numbers include lawmakers such as Rep. Elissa Slotkin, D-Mich., who joined the CIA, and Sen. Tom Cotton, R-Ark., who signed up for the infantry, as well as top Biden foreign policy officials, such as Director of National Intelligence Avril Haines.

It seems certain that in coming years the use of military force will be informed by this searing experience. U.S. foreign policy will be guided by more modest ambitions, especially when weighing the use of military power. Flournoy imagines a future in which military force is limited to more sharply defined objectives and informed by far greater humility when it comes to spreading democracy or changing societies.

In many cases, it's a vision in which force is used to manage chronic problems, rather than solve them.

Another possibility is a U.S. foreign policy that is increasingly focused more on issues such as pandemics or climate change, which require U.S. leadership and a global response. Gans noted that more than 600,000 Americans have died of covid-19, far more than the number of U.S. lives lost to terrorism and war over the past 20 years.

For now, though, it seems unlikely that these threats will take center stage in U.S. foreign policy. The Pentagon, with its $740 billion budget, still sucks up a larger share of discretionary spending than any other government agency. Meanwhile, the foreign policy establishment has shifted its focus increasingly to the competition with the likes of Russia and China.

"After 9/11 everyone raced to become a Middle East or counterterrorism expert," said Gans. "After covid, you don't see many foreign policy people racing to become global health experts."

On one subject most foreign policy experts agree: America needs to temper its faith in its armed forces. "We had so much faith in our military that we were inevitably going to overstep," said Dempsey, the Afghanistan veteran. "A military bureaucracy unchecked never yields good outcomes."