Grief, any meaningful answer to this would be ridiculously long.
In short, I suspect a conspiracy within the industrial-military-secrecy complex. National boundaries are mostly irrelevant; 9/11 looks as though powerful murderous authoritarian psychopaths arranged and facilitated an attack upon Earthly life itself. It was supremely effective. As humanity entered the new millennium, neoliberal degradation of everything biological (including human quality of life) was the most urgent issue by far. Openness and cooperation were (and remain) the most necessary responses, but 9/11 successfully generated hitherto unseen levels of conflict and suspicion.
Sorry; I’m busy now. More on this topic later.