Reactions to this massacre were swift. All commercial flights in the U.S. were grounded for three days. Fighter jets patrolled Manhattan. Wall Street stock exchanges were closed for six days, an unheard-of suspension for the lifeblood of American finances. All the while, Ground Zero smoldered as rescue workers and volunteers frantically combed through the wreckage in a search for survivors that, tragically, would be almost completely for naught.

But while the United States grieved, the world rallied around it in an unprecedented show of solidarity. French newspaper Le Monde declared, “We Are All Americans Now.” Ireland held a national day of mourning, while Canada's flags flew at half-mast for a month in commiseration. Even foes of the U.S.—including North Korea, Cuba, Libya and Iran—denounced the attacks, and the United Nations Security Council passed a resolution declaring that the United States had a right to defend itself. The world at large seemed to be standing squarely with America.

President George W. Bush's approval ratings soared to 86 percent in the days after September 11, and American flags began appearing on bumpers, porches, windows and lapels. As the US attempted to rally, on October 24, Congress passed the U.S.A. Patriot Act, aimed at rooting out terrorists at home and abroad. It greatly expanded the power and purview of American intelligence and law-enforcement agencies. Due to the actions of 19 terrorists on an early September morning, the world had changed forever.