The goal of the United States' twenty-year mission in Afghanistan evolved over time. At various points, the U.S. government hoped to
- eliminate al-Qaeda,
- decimate the Taliban movement that hosted it,
- deny all terrorist groups a safe haven in Afghanistan,
- build Afghan security forces so they could deny terrorists a safe haven in the future, and
- help the civilian government become legitimate and capable enough to win the trust of Afghans.
When each goal was met, the US government was thought to be one step closer to being able to leave.
The cost of the undertaking was enormous. The U.S. government and Department of Defense (DOD) together spent $982 billion.
The United States lost nearly 2,500 troops, while allies lost 1,200. Nearly 21,000 US troops were injured.
Afghans took a greater toll. At least 66,000 Afghan troops have been killed. More than 48,000 Afghan civilians have been killed, and at least 75,000 have been injured since 2001—both likely significant underestimations.