9.6 Challenges of the 21st Century

On September 11, 2001, 19 hijackers from the Islamist terrorist group al-Qaeda, led by Osama bin Laden, seized four airliners. They flew two into the World Trade Center towers in New York and one into the Pentagon near Washington, D.C. Passengers fought back on the fourth plane, which crashed in a Pennsylvania field. Nearly 3,000 people were killed, the deadliest foreign attack on U.S. soil.

President George W. Bush declared a war on terrorism. In October 2001 the U.S. and its allies invaded Afghanistan, whose Taliban government had sheltered al-Qaeda, and quickly drove the Taliban from power. But the fighting dragged on for two decades as the Taliban regrouped. U.S. forces killed bin Laden in Pakistan in 2011, and the last U.S. troops left Afghanistan in 2021, after which the Taliban returned to power.

Bush argued that the U.S. should strike threats before they could attack, a policy of preemption often called the Bush Doctrine. His administration claimed that Iraq's dictator, Saddam Hussein, had weapons of mass destruction (WMD) and links to terrorists. In March 2003 a U.S.-led force invaded Iraq without the approval of the UN Security Council and toppled Saddam within weeks. No stockpiles of WMD were found, and no operational partnership between Saddam and al-Qaeda was shown.

An insurgency and violence between Sunni and Shia Muslims followed. A 'surge' of additional U.S. troops in 2007 helped reduce violence, and U.S. combat forces left in 2011. Nearly 4,500 U.S. troops died, and estimates of Iraqi deaths run from more than 100,000 to several hundred thousand. Supporters said removing a brutal dictator made the region safer; critics said the war was based on faulty intelligence and drained resources from Afghanistan. The wars also cost trillions of dollars.

• USA PATRIOT Act (October 2001): passed with only one vote against in the Senate, it expanded the government's power to conduct surveillance, track phone and internet records, and share intelligence. Supporters said it closed gaps that had let the hijackers go undetected; critics, including the ACLU, said it threatened privacy and freedom of speech.
• New agencies: the Transportation Security Administration (2001) took over airport screening, and Congress created the Department of Homeland Security (2002).
• Secret surveillance: the National Security Agency's programs, revealed in 2005 and more fully by Edward Snowden in 2013, collected phone records of millions of Americans. Congress limited bulk collection in 2015.
• Detention and interrogation: suspected enemy fighters were held without trial at Guantánamo Bay, Cuba, from 2002. Photos of abuse at Iraq's Abu Ghraib prison (2004) and the use of 'enhanced interrogation' methods such as waterboarding, which critics called torture, caused outrage. The Supreme Court ruled in Boumediene v. Bush (2008) that Guantánamo detainees could challenge their detention in federal court.
• Muslim, Arab and Sikh Americans faced hate crimes and extra scrutiny, raising questions about equal treatment.

Conflicts in the oil-rich Middle East renewed arguments over how much the U.S. relied on oil, coal and gas. Scientists warned that burning oil, coal and gas was warming the planet. The U.S. signed the Kyoto Protocol (adopted 1997) on cutting greenhouse gases, but the Senate never ratified it, and U.S. participation in later climate agreements, such as the 2015 Paris Agreement, shifted with changes in administration. Supporters of action stressed the risks of climate change; opponents worried about costs to jobs and the economy. New drilling methods like fracking made the U.S. the world's largest oil and natural gas producer by the 2010s.

Despite costly wars, the 2008 financial crisis and the rise of China as an economic and military rival, the U.S. was still the world's most powerful nation after 2000, with the largest economy and by far the largest military budget.