The last United States forces left Afghanistan late on Monday, ending a 20-year occupation that began shortly after Al Qaeda’s attacks on 9/11, cost over $2 trillion, took more than 170,000 lives and ultimately failed to defeat the Taliban who allowed Al Qaeda to operate there, the New York Times reported.

The departure marks the end of a fraught, chaotic and bloody exit from the United States' longest war, according to CNN.

After nearly 2,000 U.S. troops killed in action, the pullout also raises questions about the utility of a war that saw the service of parents and then their grown children, the network said on its website.

According to the Times, Five American C-17 cargo jets flew out of Hamid Karzai International Airport in Kabul just before midnight, the officials said, completing a hasty evacuation that left behind tens of thousands of Afghans desperate to flee the country, including former members of the security forces and many who held valid visas to enter the United States.

“A new chapter of America’s engagement with Afghanistan has begun,” Secretary of State Antony J. Blinken said on Monday evening. “The military mission is over.”

But the war prosecuted by four presidents over two decades, which gave Afghans a shot at democracy and freed many women to pursue education and careers, failed in nearly every other goal. Ultimately, the Americans handed the country back to the same militants they drove from power in 2001.

Jubilant Taliban fighters and their supporters reveled in victory as the news became clear. Celebratory gunfire broke out across the city in the predawn hours on Tuesday in Kabul, the arc of tracer rounds lighting up the night sky.

“The last American soldiers departed from Kabul airport, and our country has achieved a full independence, thanks to God,” Zabihullah Mujahid, the Taliban spokesman, said on Twitter.

Control of the airport was left in the hands of the Taliban, who said they were still working on the shape of their new government.

At the airport, where scenes of mass desperation and carnage this past week became indelible images of the Americans’ final days, only a few hundred Afghans still waited at the gates on Monday night as the last flights departed.

The war began under President George W. Bush as a hunt for Al Qaeda and Osama bin Laden, the Qaeda leader who oversaw the 9/11 attacks on the United States. On that score, it succeeded: Al Qaeda was driven out and Bin Laden was killed by an American SEAL team in Pakistan in 2011.

But the United States, confident it had routed the Taliban, refused their entreaties for a negotiated surrender and plowed ahead with an enormous effort to not only drive them out but to construct a Western-style democracy in Afghanistan. The lengthy occupation allowed the Taliban to regroup, casting itself as the national resistance to the American invaders and, three American presidents later, driving them out in a war of attrition, much as Afghans had done to the Soviets in the 1980s.

The United States departure was marred by a ghastly burst of civilian casualties that seemed emblematic of the American missteps in the war.

A drone strike that the U.S. military said was aimed at thwarting an attack on the airport killed 10 civilians, survivors said, including seven children, an aid worker for an American charity organization, and a contractor with the U.S. military.

Such so-called civilian collateral damage was a primary reason so many Afghans turned against the Americans after initial good will in the early years of the U.S. intervention. In the end, the number of Afghan civilians killed in the war — more than 47,000 according to Brown University’s Cost of War project — approached the number of dead fighters.

The Taliban gave few signs on Monday that they were ready to govern a country of nearly 40 million facing a major humanitarian crisis, with about half the population malnourished, according to the United Nations.

The Taliban’s leader, the cleric and judge Haibatullah Akhundzada, remained out of sight, having issued no statement since the insurgents seized Kabul two weeks ago. One Kabul-based diplomat expressed doubt over whether he is even alive, though a Taliban spokesman insisted Mr. Akhundzada was in Kandahar, in southern Afghanistan.

“They are a little bit stunned by running a big urban center like Kabul,” a city of up to 5 million at its peak, the diplomat said, speaking on the condition of anonymity because he was not authorized to comment publicly. “They are really playing from a very weak hand.”

The diplomat said that an unresolved rift between the group’s moderates, like the political chief, Abdul Ghani Baradar, who led the negotiations with the United States, and hard-liners like the Haqqani brothers, the military leaders, was further weakening the ex-insurgents.

The claim that the American drone strike on Sunday caused civilian casualties would be, if confirmed, a bitter parting legacy of the military intervention.

On Monday, a spokesman for the U.S. Central Command reaffirmed an earlier statement that the military hit a valid target, an explosives-laden vehicle it said was driven by operatives of the Afghan affiliate of the Islamic State, known as Islamic State Khorasan or ISIS-K, and which posed an “imminent” threat to the airport. ISIS-K claimed responsibility for a suicide attack that killed more than 170 people, including 13 American service members, at the airport on Thursday.