Ceremonies across the United States on September 11 marked a quarter-century since hijackers flew passenger planes into the World Trade Center and the Pentagon, killing nearly 3,000 people in a single morning. Mourners gathered at memorial sites to read the names of the dead.
The 2001 attacks triggered a series of American-led military campaigns that reshaped the map of conflict for a generation. Successive wars launched under the banner of the “war on terror” have killed at least 4.5 million people, according to figures compiled from research on the human cost of the conflicts.
More than 38 million people have been displaced by the fighting, uprooted from homes across several countries. The campaigns extended well beyond the initial invasions, drawing in air operations, drone strikes and prolonged occupations.
US forces have carried out bombing operations somewhere every year since 2001, an analysis mapping the reach of the campaigns found. Afghanistan, Iraq, Pakistan, Somalia, Syria and Yemen were among the countries struck across the 25-year span.
The wars also produced a lasting legal and security order. Surveillance powers, indefinite detention and expanded executive authority introduced after the attacks remain in force, drawing continued criticism from rights advocates who argue the framework should be dismantled.
The financial toll ran into the trillions of dollars, absorbed by successive US administrations. The conflicts stretched across the tenures of four presidents and outlasted the withdrawal of American troops from Afghanistan in 2021.
Beyond the direct casualties, researchers count deaths from the collapse of infrastructure, health systems and food supplies in war-affected regions. Displacement waves reached neighbouring states and beyond, with many refugees never returning home.
Related conflicts continue to drive fresh displacement across the wider region. A recent surge in fighting across the Middle East forced more than 330,000 people from their homes, adding to the long tally of uprooted populations.
At the New York memorial, relatives paused at the reflecting pools built where the twin towers once stood. Similar observances took place at the Pentagon and at the Flight 93 site in Pennsylvania, where a plane crashed after passengers confronted the hijackers.
The 25th anniversary arrived with the security architecture built after the attacks still largely intact, and with debate over its human and legal cost unresolved.