Twenty-five years have passed since the 9/11 attacks that reshaped global geopolitics, when 19 al-Qaeda hijackers seized four commercial airliners and crashed them into the World Trade Center in New York and the Pentagon in Washington D.C., killing nearly 3,000 people. What followed that fateful day was a generation of continuous, U.S.-led military conflicts that have left an unrivaled trail of human suffering and economic burden, new data from the Brown University Watson Institute’s Cost of War project confirms. These post-9/11 conflicts have killed an estimated 4.5 to 4.7 million people directly and indirectly, and displaced more than 38 million others across multiple regions of the world.
Less than one month after the 9/11 attacks, then-U.S. President George W. Bush launched what he dubbed the ‘War on Terror’, beginning with the October 2001 invasion of Afghanistan codenamed Operation Enduring Freedom. The Taliban regime collapsed within weeks, but the conflict dragged on for nearly 20 years across four consecutive U.S. presidencies, making it the longest war in U.S. history. The Cost of War project estimates that 176,000 people died directly from combat in Afghanistan, with hundreds of thousands more killed indirectly by starvation, preventable disease, and untreated injuries. Food insecurity surged from 62 percent before the invasion to 92 percent after, and unexploded ordnance and landmines continue to maim and kill Afghan civilians decades later. In 2021, as the last U.S. troops withdrew, the Taliban retook control of the country, leaving a fractured nation still grappling with the legacy of war.
Just under two years after the Afghanistan invasion, in March 2003, the U.S. launched its invasion of Iraq, built on the false claim that former Iraqi leader Saddam Hussein possessed weapons of mass destruction. For Iraqis who lived through the invasion, the trauma remains unresolved decades later. ‘Everything changed,’ recalled Omar, an 18-year-old university student in Baghdad at the time of the invasion, in an interview with Al Jazeera. ‘We remember the sound of the bombs; we were so afraid. Some of my friends ignored warnings to stay inside and went to see what was happening when the fighting reached the city. I asked them why they would go. They left, and they never came back. It is still devastating to think about.’ According to project data, 315,000 people died directly from combat in Iraq, with millions more dying indirectly from the collapse of healthcare, food systems, and infrastructure. Today, more than two decades after the invasion, over one million Iraqis remain displaced from their homes.
Beyond the two large-scale ground wars in Afghanistan and Iraq, the U.S. expanded the ‘War on Terror’ into a sprawling network of air and drone strikes across the Middle East, South Asia, and Africa, operating in at least 10 countries over 25 years. Data from the London-based non-profit Airwars, which tracks civilian casualties from military operations, and the Bureau of Investigative Journalism documents the scale of these campaigns: since 2004, the U.S. has carried out 423 strikes in Pakistan that killed an estimated 2,499 to 4,001 people, including between 424 and 966 civilians; at least 186 strikes and raids in Yemen have killed at least 853 people, 158 of them civilians; between 2001 and 2016, 19 to 23 strikes in Somalia killed 188 to 276 people. In 2011, the U.S. led a NATO air campaign under a UN civilian protection mandate to oust former Libyan leader Muammar Gaddafi, carrying out nearly 9,700 strikes over seven months before Gaddafi was captured and killed by rebels. In 2014, the U.S. launched Operation Inherent Resolve against the Islamic State in Iraq and Syria, which relied on heavy air and ground operations that deployed tens of thousands of bombs. While U.S. officials have acknowledged just 1,417 civilian deaths from that campaign, Airwars estimates the true number is between 8,264 and 13,360.
Across all conflict zones affected by post-9/11 wars, the scale of displacement is unprecedented in modern history, exceeding any other conflict since the start of the 20th century. The Cost of War project estimates that more than 38 million people across Afghanistan, Iraq, Pakistan, Yemen, Somalia, the Philippines, Libya, and Syria have been displaced, either crossing international borders or forced to flee their homes within their own countries. Decades after the initial invasions, displacement continues to uproot communities. Last year alone, Iran and Pakistan forced roughly 2.9 million Afghan refugees to return to Afghanistan, a country still ravaged by conflict and economic collapse. For many Afghans, repeated displacement has become a permanent way of life. Ayesha, a 40-year-old Afghan mother, has spent most of her life moving between Afghanistan and Iran due to repeated conflict. Her family first fled Afghanistan in 1994, returned in 2000, then fled again in 2002 after the U.S. invasion. After living in Iran for 11 years, she and her children were deported back to Afghanistan. ‘I have gone back and forth so many times,’ Ayesha explained. ‘This last time we stayed 11 years, but then the Iranians deported us and kicked my children out of school. We have no home to call our own anymore.’ (Omar and Ayesha are pseudonyms used to protect their privacy.)
The human cost of the post-9/11 wars extends beyond civilian populations in conflict zones, extending to U.S. and coalition military personnel and veterans who served in the conflicts. Nearly 3,500 coalition troops have been killed in Afghanistan and Iraq, with more than 23,500 wounded. In Afghanistan alone, 2,500 U.S. troops died and 20,000 were wounded before the 2021 withdrawal; in Iraq, 3,481 U.S. troops died and more than 31,000 were wounded. The long-term costs for veterans are staggering, and a public health crisis of mental illness and suicide persists. By 2050, the Cost of War project projects that healthcare and benefits for post-9/11 veterans will cost the U.S. between $2.2 trillion and $2.5 trillion, much of which remains unfunded. ‘Four times as many U.S. service members and veterans have died by suicide as have died in combat during post-9/11 wars,’ said Stephanie Savell, director of the Cost of War project. ‘Veterans return with far higher rates of PTSD and traumatic injury, and are deployed more frequently than in past conflicts. The costs of war are borne by a small segment of the U.S. population, rather than shared by the public as a whole.’
In total, the U.S. has spent an estimated $5.8 trillion on 25 years of post-9/11 conflicts, with $2.2 trillion more earmarked for future veteran care, bringing the total cost to at least $8 trillion and rising. By 2030, the U.S. will have paid as much in interest on war-related debt as it spent on combat operations themselves, a debt that will be carried by Americans under 25 for decades to come. Public opinion polling shows most Americans oppose endless aggressive foreign wars, and the ongoing conflict in the region remains deeply unpopular with U.S. voters. Savell noted that many voters supported former President Donald Trump in part because he promised to end ‘endless wars’ and campaigned on a platform of peace, but his administration oversaw a sharp expansion of U.S. military violence. ‘That promise has been completely broken since he took office,’ Savell explained. ‘Drone strikes intensified in Somalia and Yemen, rules of engagement were loosened to allow more civilian casualties, and less protection for civilian lives. Beyond launching a new war in Iran, expanded strikes in the Caribbean, U.S. military violence has intensified across the globe.’