Between 8:46 a.m. and 10:28 a.m. on Sept. 11, 2001, 19 al-Qaeda terrorists turned four passenger aircraft into weapons. Two planes struck the World Trade Center in New York. A third hit the Pentagon. The fourth crashed in Pennsylvania after passengers and crew fought back. The attacks killed 2,977 people.JOIN US ON TELEGRAMFollow our coverage of the war on the @Kyivpost_official. Twenty-five years later, relatives again gathered at Ground Zero to read every victim’s name. The ceremony included moments of silence marking the attacks’ timeline and, for the first time, another silence for those who later died after exposure to toxic dust, the Associated Press reported. The attacks changed airport security, expanded surveillance, and began wars whose consequences still shape US politics. They also forced NATO to answer a question it had spent half a century trying to deter: What does the promise that an attack on one ally is an attack on all require in practice? What Article 5 delivered On Sept. 12, 2001, NATO allies agreed that the attacks would fall under Article 5 if investigators established that they had been directed from abroad. The alliance confirmed that finding on Oct. 2. It remains the first and only invocation of NATO’s collective-defense clause. Article 5 is often summarized as an automatic military response. However, its wording is more flexible. Every member must assist an ally under attack, but each decides what action it considers necessary. Assistance may or may not include armed force, and national constitutional requirements still apply.