9/11 was the worst single terrorist incident of all time. On one day 3,000 innocent people were killed. A military response from the US was necessary.
9/11 directly caused two wars: the Afghanistan War and the Second Iraq War. I believe the US was right to go into Afghanistan and topple the jihadi training camps, bomb Al Qaeda there and dismantle the Taliban. The Taliban had given a murderous Osama bin Laden refuge. A few years earlier, bin Laden had declared war on America. Nobody took any notice because at the time he came across as an Arab crackpot. Well, it turned out he was deadly serious. The US seal team was totally justified in shooting him dead in 2010.
However, I believe the US was wrong to attack Iraq. Saddam Hussein was a typical Arab dictator. A nasty person but he had nothing to do with Al Qaeda or Islamic terrorism. Both the US & the UK were wrong to invade Iraq.