For anyone under 30 years old, it must be difficult to fully appreciate the fear that gripped the United States after September 11, 2001. On that terrible day, millions of Americans witnessed airplanes flying into buildings, people jumping off skyscrapers, and the Twin Towers collapsing with thousands of innocents inside. The months and years that followed saw deadly anthrax attacks; attempted bombings of airliners with explosives hidden in shoes, underwear, and soft drink containers; terrorist atrocities in Bali, Istanbul, Jakarta, London, Madrid, Mumbai, and elsewhere; the use of vehicles to plow into pedestrians; and a regular stream of shootings and stabbings. For much of the decade that followed 9/11, the question for most Americans was not if, but when, the next major terrorist attack on American soil would take place.

Peter Bergen’s All the Presidents’ Wars chronicles the fateful decisions and events that were shaped by those fears. The terrorists hijacked not just airplanes but also the direction of U.S. foreign policy. Disavowing the need for Washington to be the world’s policeman, President George W. Bush was elected in 2000 on a platform of conducting what he called a “humble” foreign policy, his realism summed up by Condoleezza Rice, his national security adviser: “We don’t need to have the 82nd Airborne escorting kids to kindergarten.” Yet by 2003, that very division found itself not escorting kids but spearheading an invasion of Iraq designed to transform and democratize the entire Middle East. Singularly focused on the need to prevent another 9/11, Bush’s modest approach to world affairs morphed into the so-called global war on terror that became the primary paradigm for U.S. foreign policy, akin to the role of the Cold War from 1947 until 1989.

Bush launched the war on terror, but he was hardly the last president to wage it. Barack Obama, although skeptical of U.S. military intervention and elected in part because of his opposition to the Iraq war, found himself not just fighting but expanding the war in Afghanistan—where between 2009 and 2012 he ordered a surge of nearly 50,000 additional U.S. troops (bringing the total to around 100,000)—and turning lethal drone warfare from a novel tactic into a routine tool. In May 2011, U.S. special forces finally killed Osama bin Laden, the architect of 9/11, but the war on terror was far from over. Three years later, the Islamic State in Iraq and Syria, also known as ISIS, a group that Obama had initially disparaged as a terrorist “JV team,” declared a “caliphate” and waged a savage campaign of killing, ethnic cleansing, kidnapping, and rape—leading to another multiyear U.S.-led military intervention in the region.

Donald Trump, a critic of foreign interventions (at least for campaign purposes), was first elected president in 2016 hoping to de-prioritize the war on terror but, like his predecessors, failed to do so. In August 2017, Trump said his “original instinct” was to pull out of Afghanistan entirely, but that “decisions are much different when you sit behind the desk in the Oval Office.” He agreed with his military advisers to shift to a “conditions based” withdrawal, the same strategy that had kept U.S. troops in Afghanistan since 2011. Similarly on Syria, Trump twice announced plans to withdraw U.S. troops but never fully executed them, primarily because of institutional resistance from those concerned about the enduring need to contain ISIS. His administration continued to conduct drone strikes and special operations raids in Afghanistan, Iraq, Somalia, Syria, and Yemen, often with looser rules of engagement than in the past.

Thus did Joe Biden, in January 2021, become the fourth U.S. president since 9/11 to find counterterrorism—and the war in Afghanistan in particular—intruding on his initial foreign policy agenda even as he tried to deal with other big strategic challenges. Biden inherited from Trump a deal with the Taliban that included a commitment to withdraw all U.S. troops from Afghanistan, but it was left to Biden to implement it. He did so, but at great cost. Without the backing of U.S. and other allied troops, the Afghan government quickly collapsed, allowing the Taliban to take over the country almost exactly 20 years after they were expelled from power. The chaotic........

© Foreign Affairs