On August 15, 2021—just two weeks before U.S. troops were set to officially withdraw from Afghanistan—Taliban leaders enter the capital city of Kabul and sweep back into power with little resistance. The Afghan government collapses, the country’s president Ashraf Ghani flees, and many desperate Afghan civilians are left behind.

The withdrawal ended a two-decade war that began in 2001 after the 9/11 terrorist attacks with the aim to destroy Al Qaeda, the terrorist group behind the attacks, and oust the Taliban that was refusing to hand over mastermind Osama bin Laden to the U.S. On August 16, President Biden, harshly criticized by many for the decision, gave a speech defending the withdrawal, and calling the Afghanistan operation “America’s Longest War.”

“I cannot and I will not ask our troops to fight on endlessly in…another country’s civil war, taking casualties, suffering life-shattering injuries, leaving families broken by grief and loss,” Biden said. “This is not in our national security interest. It is not what the American people want. It is not what our troops, who have sacrificed so much over the last two decades, deserve.”

The Afghanistan operation claimed the lives of 2,448 American military members, 3,846 U.S. contractors, and more than 100,000 Afghans.

Leaving Afghanistan two decades after 9/11 involved both the Donald Trump and Biden administrations. Both presidents expressed eagerness to withdraw from Afghanistan and end the war. The Trump administration negotiated a withdrawal with the Taliban set a deadline of May 1, 2021 and reduced U.S. troop numbers from about 13,000 to 2,500. Biden delayed that deadline to August 31.

Meanwhile, the Taliban was not complying with the agreement and was continuing to attack Afghan government forces. Still, U.S. intelligence did not anticipate such a swift collapse of the Afghan government to the Taliban extremists.

In June of 2021, officials said that Kabul could capitulate within six to 12 months. The collapse within hours stunned many people and left them unprepared. Within days, the Taliban tore down or defaced billboards depicting women, and Afghan flags were lowered.

Anthony H. Cordesman, a former consultant to the State and Defense departments on Afghanistan, told The Washington Post that the rush to flee Kabul was so chaotic because “down to the final days of collapse, people were in denial.”

Videos circulating in the news showed the chaos in Afghanistan during and after the withdrawal, including footage showing the Taliban celebrating its return to power with gunfire, and footage showing desperate Afghans chasing and clinging to departing American military planes at the Kabul airport.

Less than two weeks after the withdrawal, nearly 200 people—including 13 remaining U.S. service members—died at the Kabul airport perimeter in a suicide attack. The Islamic State-Khorasan claimed responsibility for the massacre on August 26.