It wasn’t the events of September 11th that changed the world, but the events of September 12th and beyond, when the Bush administration took the world to war in response; that changed the world, and continues to threaten U.S. and global security, and shred U.S. democracy.
The brutality of ISIS has led many to argue that only military action can stop them. Phyllis Bennis, fellow of Transnational Institute and a long-term observer and analyst of US foreign policy in the Middle East, argues that US occupation and military action was the principal cause of ISIS rise and therefore cannot be the solution. She outlines alternative options for constraining the advance of ISIS and bringing peace back to the troubled countries of Iraq and Syria. See also Phyllis' primer, Understanding ISIS and the new global war on terror
The UN has huge role to play in Afghanistan, but when it is trying to do this under the conditions of occupation it is inevitable that it is going to be seen as part of that occupation, not as part of the solution.
Ten years and two wars later, Americans face the monetary and psychological costs of both militarism and Wall Street materialism, effectively bankrupting the country; not to mention the casualties of war at home, and in Afghanistan and Iraq.