It was also preceded by a violent act of terrorism

Its so easy for people to forget the decades of violent acts committed in and around the Saudi Peninsula, and fixate instead on a handful of retaliatory strikes against US interests. The Battle of Mogadeshu, which involved Black Hawk helicopters obliterating Somali mosques with hellfire missiles. The brutal occupation of the Northern Alliance in Afghanistan, from 1992 to 2001 as a US-backed narco-state. The entire Iran-Iraq War, sponsored by US arms dealers and double-dealing diplomats, which resulted in the deaths of hundreds of thousands of Arab and Persian young people. The occupation of Saudi Arabia by a western-backed military dictatorship going back nearly a century. The violent overthrow of democracies from Indonesia to Egypt in pursuit of neoliberal international trade policy.

9/11 didn't happen in a vacuum any more than the Brian Thompson assassination or the aborted coup in South Korea. These have long historical tails that trace back to a geopolitical policy that's racked up a staggering death toll.

To quote Mark Twain:

There were two "Reigns of Terror," if we would but remember it and consider it; the one wrought murder in hot passion, the other in heartless cold blood; the one lasted mere months, the other had lasted a thousand years; the one inflicted death upon ten thousand persons, the other upon a hundred millions; but our shudders are all for the "horrors" of the minor Terror, the momentary Terror, so to speak; whereas, what is the horror of swift death by the axe, compared with lifelong death from hunger, cold, insult, cruelty, and heart-break? What is swift death by lightning compared with death by slow fire at the stake? A city cemetery could contain the coffins filled by that brief Terror which we have all been so diligently taught to shiver at and mourn over; but all France could hardly contain the coffins filled by that older and real Terror—that unspeakably bitter and awful Terror which none of us has been taught to see in its vastness or pity as it deserves.