At least 800,000 people have been killed by direct war violence in Iraq, Afghanistan, Syria, Yemen, and Pakistan. The number of people who have been wounded or have fallen ill as a result of the conflicts is far higher, as is the number of civilians who have died indirectly as a result of the destruction of hospitals and infrastructure and environmental contamination, among other war-related problems.
Thousands of United States service members have died in combat, as have thousands of civilian contractors. Many have died later on from injuries and illnesses sustained in the war zones. Hundreds of thousands of soldiers and contractors have been wounded and are living with disabilities and war-related illnesses. Allied security forces have also suffered significant casualties, as have opposition forces.
However, the vast majority of people killed are civilians. More than 310,000 civilians have been killed in the fighting.
Millions of people living in the war zones have also been displaced by war. To date, over 8.4 million Afghans, Pakistanis, and Iraqis are living as war refugees in other countries or are displaced from their homes. An additional 12.6 million Syrians are displaced, many as a result of the US war against the Islamic State in Syria.
The US could have pursued several nonmilitary alternatives to holding accountable those responsible for perpetrating the 9/11 attacks. These alternatives would have been far less costly in human lives. For example, the US invasion of Iraq has turned the country into a laboratory in which militant groups such as Islamic State have been able to hone their techniques of recruitment and violence. The formation of jihadi groups now spreading throughout the region counts among the many human costs of that war.
(Page updated as of January 2020)