Peshawar sits at the eastern mouth of the Khyber Pass, roughly 48 kilometers from the Afghan border. For centuries it has been a crossroads between Central and South Asia, a city whose Bala Hisar fortress has watched armies come and go for over two thousand years. But the violence of the 21st century was different. The Tehrik-i-Taliban Pakistan, or TTP, had waged an insurgency against the Pakistani state since 2007, and Peshawar bore the brunt. Suicide bombings at bazaars, attacks on churches, explosions in crowded markets. In June 2014, the Pakistan Armed Forces launched Operation Zarb-e-Azb against TTP strongholds in North Waziristan. The offensive was succeeding militarily, and the militants wanted retaliation that would break the nation's resolve. They chose a school full of children.

The six attackers, all foreign nationals -- one Chechen, three Arabs, and two Afghans -- entered through the school's rear. They carried AK-47s, grenades, and wore suicide vests. Their first target was the school auditorium, where they opened fire indiscriminately on students attending the first-aid course. A teacher was set on fire in front of her students. Classrooms became killing fields as the gunmen moved methodically through the building, shooting children as young as eight at point-blank range. Pakistan Army commandos from the Special Services Group launched a rescue operation, fighting room by room through the school complex. By the time the last gunman was killed at around 6 p.m., 149 people lay dead. One hundred and thirty-two of them were children between the ages of eight and eighteen. More than 120 others were wounded. The attackers had come not to take hostages or make demands, but simply to kill as many children as possible.

The TTP had miscalculated. Rather than breaking Pakistan's will, the massacre unified a fractured nation in grief and fury. Prime Minister Nawaz Sharif declared three days of national mourning. Imran Khan, then leading an ongoing protest march against the government, immediately called it off. Malala Yousafzai, herself shot by the TTP in 2012, said she was "heartbroken by this senseless and cold-blooded act of terror." Even al-Qaeda's spokesman declared that "our hearts are bursting with pain" and insisted soldiers should be targeted, never children. Candlelight vigils spread from Islamabad to London. International media called it Pakistan's 9/11, and the comparison felt apt. The massacre shattered whatever residual sympathy the TTP enjoyed in Khyber Pakhtunkhwa. Public opinion, which had been ambivalent toward the insurgency in regions where government support was thin, turned decisively against the militants.

Pakistan's response was swift and far-reaching. Within days, the Pakistan Air Force launched strikes against TTP positions in the Tirah Valley using F-16s and JF-17s, while CIA drone strikes hit militant targets in eastern Afghanistan and North Waziristan. On the ground, intelligence agencies tracked down and killed TTP operatives across the country, from Quetta to Karachi to Khyber Agency. The government lifted its moratorium on the death penalty for terrorism cases, and Parliament unanimously passed the 21st Constitutional Amendment in January 2015, establishing military courts for speedy terrorism trials. The Army Public School itself reopened on 12 January 2015 under heavy military guard. General Raheel Sharif, the Chief of Army Staff, personally attended the first morning assembly. The mastermind of the attack, Khalid Khurasani, evaded justice until 9 July 2016, when a U.S. drone strike killed him in Nangarhar Province, Afghanistan.

Pakistan moved its Children's Day to 16 December beginning in 2015. Each year, anniversary ceremonies are held at the school, where portraits of the victims line the walls and the road leading into the city. Parents gather alongside military officers, their grief undiminished by time. The musician Ali Zafar partnered with The Citizens Foundation to establish 141 Schools for Peace, one dedicated to each confirmed victim. In 2015, 107 schools across Khyber Pakhtunkhwa were renamed after the children who died. The massacre remains a wound that refuses to close, a before-and-after moment in the national consciousness. It ended Pakistan's equivocation about the insurgency and forged a consensus that the state would fight rather than negotiate with the TTP. That consensus came at the highest possible price: the lives of 132 children who went to school one December morning and never came home.