The longest war in United States history. Launched in response to the September 11, 2001 attacks, the conflict aimed to dismantle al-Qaeda, remove the Taliban from power, and later build a stable Afghan government. It lasted nearly 20 years, involved a broad international coalition, and ended with the Taliban’s return to power in August 2021.
On 11 September 2001, al-Qaeda terrorists hijacked four airliners and attacked the World Trade Center and the Pentagon, killing nearly 3,000 people. The group was based in Afghanistan under the protection of the Taliban regime.
The Taliban, a hardline Islamist movement, controlled most of Afghanistan after the civil war that followed the Soviet withdrawal. They provided sanctuary to Osama bin Laden and al-Qaeda while imposing a strict interpretation of Islamic law.
The United States demanded that the Taliban hand over bin Laden and shut down al-Qaeda camps. When the Taliban refused, the U.S. and coalition partners prepared military action under the banner of self-defense and the UN-authorized campaign against terrorism.
Afghanistan had already endured decades of conflict: the Soviet invasion (1979–1989), subsequent civil war, and Taliban consolidation. The country was one of the poorest and most heavily armed places on earth, with deep ethnic and tribal divisions.
U.S. and British forces launch air strikes. Special operations forces and CIA teams work with the Northern Alliance. The Taliban regime collapses within weeks; Kabul falls in November.
International conference establishes an interim Afghan government led by Hamid Karzai. A new constitution and elections follow in subsequent years.
The Taliban regroups in Pakistan and southern/eastern Afghanistan. Suicide bombings, IEDs, and guerrilla tactics increase. NATO expands its mission beyond Kabul.
President Obama orders a major troop increase. Peak U.S. presence exceeds 100,000. Focus on counterinsurgency, protecting population centers, and training Afghan forces. Osama bin Laden is killed in Pakistan in May 2011.
Responsibility for security gradually shifts to Afghan forces. NATO combat mission formally ends in December 2014; Resolute Support begins as a train-advise-assist mission.
The Trump administration signs a deal in Doha for the withdrawal of U.S. troops in exchange for Taliban commitments on counterterrorism and talks with the Afghan government.
Afghan government forces collapse rapidly. The Taliban enter Kabul on 15 August. Chaotic evacuation from Hamid Karzai International Airport follows. The last U.S. forces leave on 30 August 2021.
Rapid removal of the Taliban, establishment of a new government, and initial reconstruction efforts. Al-Qaeda leadership flees to Pakistan. Optimism about nation-building is high.
Taliban resurgence, heavy fighting in the south and east, troop surge under Obama, and gradual transition of security responsibility to Afghan forces. Highest coalition casualties occur in this period.
Reduced international presence, continued Taliban pressure, peace talks, and the final rapid collapse of the Afghan Republic in the summer of 2021 as foreign forces departed.
The mission evolved from a narrow goal of destroying al-Qaeda and removing the Taliban into a far broader effort to build Afghan institutions, security forces, and a democratic government—goals that proved extremely difficult in a fragmented society with limited state capacity.
Taliban and Haqqani Network leaders operated from across the border in Pakistan for much of the war. This external sanctuary complicated military efforts and remained a persistent strategic problem for the coalition.
Billions were spent training and equipping the Afghan National Army and police. While some units fought effectively, the forces suffered from high attrition, corruption, poor logistics, and dependence on foreign air support and funding.
Civilian casualties from airstrikes, night raids, and the broader fighting eroded support among some Afghans. Corruption within the Afghan government further undermined the legitimacy of the U.S.-backed state.
The War in Afghanistan began as a focused response to the 9/11 attacks and the Taliban’s harboring of al-Qaeda. It expanded into a prolonged effort to stabilize and rebuild a country with deep historical, ethnic, and geographic challenges. Despite tactical military successes and significant investment, the Afghan government and security forces proved unable to stand without sustained foreign support. The rapid collapse in 2021 marked the end of the longest war in American history and left the Taliban once again in control of Afghanistan.