The United States launched the war in Afghanistan following the September 11, 2001 terrorist attacks. The conflict lasted two decades and spanned four U.S. presidencies, becoming the longest war in American history.

By August 2021, the war began to come to a close with the Taliban regaining power two weeks before the United States was set to withdraw all troops from the region. Overall, the conflict resulted in tens of thousands of deaths and a $2 trillion price tag. Here's a look at key events from the conflict.

War on Terror Begins

Investigators determined the 9/11 attacks—in which terrorists hijacked four commercial airplanes, crashing two into the World Trade Center towers in New York City, one at the Pentagon near Washington, D.C., and one in a Pennsylvania field—were orchestrated by terrorists working from Afghanistan, which was under the control of the Taliban, an extremist Islamic movement. Leading the plot that killed more than 2,700 people was Osama bin Laden, leader of the Islamic militant group al Qaeda. It was believed the Taliban, which seized power in the country in 1996 following an occupation by the Soviet Union, was harboring bin Laden, a Saudi, in Afghanistan.

In an address on September 20, 2001, President George W. Bush demanded the Taliban deliver bin Laden and other al Qaeda leaders to the United States, or "share in their fate." They refused.

On October 7, 2001, U.S. and British forces launched Operation Enduring Freedom, an airstrike campaign against al Qaeda and Taliban targets including Kandahar, Kabul and Jalalabad that lasted five days. Ground forces followed, and with the help of Northern Alliance forces, the United States quickly overtook Taliban strongholds, including the capital city of Kabul, by mid-November. On December 6, Kandahar fell, signaling the official end of Taliban rule in Afghanistan and causing al Qaeda, and bin Laden, to flee.

Shift to Reconstruction

During a speech on April 17, 2002, Bush called for a Marshall Plan to aid in Afghanistan’s reconstruction, with Congress appropriating more than $38 billion for humanitarian efforts and to train Afghan security forces. In June, Hamid Karzai, head of the Popalzai Durrani tribe, was chosen to lead the transitional government.

While approximately 8,000 American troops remained in Afghanistan as part of the International Security Assistance Force (ISAF) overseen by NATO, the U.S. military focus turned to Iraq in 2003, the same year U.S. Secretary of Defense Donald Rumsfeld declared "major combat" operations had come to an end in Afghanistan.

A new constitution was soon enacted and Afghanistan held its first democratic elections since the onset of the war on October 9, 2004, with Karzai, who went on to serve two five-year terms, winning the vote for president. The ISAF’s focus shifted to peacekeeping and reconstruction, but with the United States fighting a war in Iraq, the Taliban regrouped and attacks escalated.

Troop Surge Under Obama

In a written statement released February 17, 2009, newly elected President Barack Obama pledged to send an extra 17,000 U.S. troops to Afghanistan by summer to join 36,000 American and 32,000 NATO forces already deployed there. "This increase is necessary to stabilize a deteriorating situation in Afghanistan, which has not received the strategic attention, direction and resources it urgently requires," he stated. American troops reached a peak of approximately 110,000 soldiers in Afghanistan in 2011.

In November 2010, NATO countries agreed to a transition of power to local Afghan security forces by the end of 2014, and, on May 2, 2011, following 10-year manhunt, U.S. Navy SEALs located and killed bin Laden in Pakistan.

President Barack Obama, Vice President Joe Biden, Secretary of State Hillary Clinton and members of the national security team receive an update on the mission against Osama bin Laden in the Situation Room of the White House May 1, 2011, Washington, D.C.

President Barack Obama, Vice President Joe Biden, Secretary of State Hillary Clinton and members of the national security team receive an update on the mission against Osama bin Laden in the Situation Room of the White House May 1, 2011, Washington, D.C.

Following bin Laden's death, a decade into the war and facing calls from both lawmakers and the public to end the war, Obama released a plan to withdraw 33,000 U.S. troops by summer 2012, and all troops by 2014. NATO transitioned control to Afghan forces in June 2013, and Obama announced a new timeline for troop withdrawal in 2014, which included 9,800 U.S. soldiers remaining in Afghanistan to continue training local forces.

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Trump: 'We Will Fight to Win'

In 2015, the Taliban continued to increase its attacks, bombing the parliament building and airport in Kabul and carrying out multiple suicide bombings.

In his first few months of office, President Donald Trump authorized the Pentagon to make combat decisions in Afghanistan, and, on April 13, 2017, the United States dropped its most powerful non-nuclear bomb, called the "mother of all bombs," on a remote ISIS cave complex.

In August 2017, Trump delivered a speech to American troops vowing "we will fight to win" in Afghanistan. "America's enemies must never know our plans, or believe they can wait us out," he said. "I will not say when we are going to attack, but attack we will."

The Taliban continued to escalate its terrorist attacks, and the United States entered peace talks with the group in February 2019. A deal was reached that included the U.S. and NATO allies pledging a total withdrawal within 14 months if the Taliban vowed to not harbor terrorist groups. But by September, Trump called off the talks after a Taliban attack that left a U.S. soldier and 11 others dead. “If they cannot agree to a ceasefire during these very important peace talks, and would even kill 12 innocent people, then they probably don’t have the power to negotiate a meaningful agreement anyway,” Trump tweeted.

Still, the United States and Taliban signed a peace agreement on February 29, 2020, although Taliban attacks against Afghan forces continued, as did American airstrikes. In September 2020, members of the Afghan government met with the Taliban to resume peace talks and in November Trump announced that he planned to reduce U.S. troops in Afghanistan to 2,500 by January 15, 2021.

Withdrawal of US Troops

The fourth president in power during the war, President Joe Biden, in April 2021, set the symbolic deadline of September 11, 2021, the 20th anniversary of the 9/11 attacks, as the date of full U.S. withdrawal from Afghanistan, with the final withdrawal effort beginning in May.

Facing little resistance, in just 10 days, from August 6-15, 2021, the Taliban swiftly overtook provincial capitals, Kandahar, Mazar-e-Sharif and, finally, Kabul. As the Afghan government collapsed, President Ashraf Ghani fled to the UAE, the U.S. embassy was evacuated and thousands of citizens rushed to the airport in Kabul to leave the country.

By August 14, Biden had temporarily deployed about 6,000 U.S. troops to assist in evacuation efforts. Facing scrutiny for the Taliban's swift return to power, Biden stated, “I was the fourth president to preside over an American troop presence in Afghanistan—two Republicans, two Democrats. I would not, and will not, pass this war on to a fifth.”

During the war in Afghanistan, more than 3,500 allied soldiers were killed, including 2,448 American service members, with 20,000-plus Americans injured. Brown University research shows approximately 69,000 Afghan security forces were killed, along with 51,000 civilians and 51,000 militants. According to the United Nations, some 5 million Afghanis have been displaced by the war since 2012, making Afghanistan the world's third-largest displaced population.

Sources

The U.S. War in Afghanistan, Council on Foreign Relations

Costs of the Afghanistan war, in lives and dollars, Associated Press

Who Are the Taliban, and What Do They Want?, The New York Times

Operation Enduring Freedom Fast Facts, CNN

Afghanistan: Why is there a war?, BBC News

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