“As an act of terrorism, 9/11 was a resounding success. The U.S. responded by decimating al-Qaida, but the organization survived in a weakened form. The Syrian civil war and the weakness of the Iraqi state provided new opportunities. Three offshoots of al-Qaida — al-Qaida in Iraq, the Islamic State group (ISIS), and Jabhat al-Nusra — came to play major roles in the first two decades of the 21st century. Abu Musab al-Zarqawi’s group contributed to turning the U.S. occupation of Iraq into a quagmire and sharpening Sunni-Shia tensions in the country and region. ISIS used territorial control on both sides of the Iraqi-Syrian border to declare a caliphate and launch or inspire deadly terrorist attacks from the region to Europe to North America and the Indo-Pacific. A large international coalition built and led by the United States destroyed that ‘state,’ but as we have seen the jihadi group is still with us. And in Idlib province in Syria, a large contingent of Jabhat al-Nusra fighters controls a significant swath of land. Meanwhile, 20 years after 9/11 and the invasion of Afghanistan, a local branch of ISIS poses a significant terrorist threat, as its August 26 [2021] attack on Afghan civilians and U.S. troops at the airport in Kabul shows.”
– Itamar Rabinovich, “Reflections on the long-term repercussions of September 11 for US policy in the Middle East,” brookings.edu, Tuesday, September 7, 2021