Following the terrorist attacks of September 11, 2001, US President George W. Bush demanded that Afghanistan's Taliban government surrender Osama bin Laden and end support for al-Qaeda. The Taliban refused.
On October 7, US bombs began falling on Taliban forces. NATO allies quickly pledged support for the US, and US boots hit the ground in Afghanistan two weeks later.
Thus began a war, now the longest in US history, that has killed more than 3,500 coalition soldiers and 110,000 Afghans. It has cost the American taxpayer nearly $3 trillion. US allies have also made human and material sacrifices.