My first thought was you reap what you sow. The good old US of A had spent a century or more bringing war and devastation to a good part of the world in support of their own economy. It finally came home on a very small scale compared to what they did to Iran, Vietnam, the Caribbean, Central and South America. My second thought was they are going to start another war they can't win but that will make a lot of very wealthy people even wealthier and keep the have nots rallying around the flag.
This is how it works for USA.
You find a country with oil or the one that is strategic in terms of military.
In that country, you fund a group to create an unrest.
You give it arms, Israel joins you. In the meantime, Russia arms the other side. (So both sides are making money by selling arms)
The rebellion group becomes powerful.
Time to brand them terrorists.
US invades the nation. Controls the oil supply and oil field (Iraq). Leaves some army there(peace keeping).
Now US has army presence in another corner of the world.
It has happened over and over again esp during Republicans regime.
Prime example is Taliban. During cold war, US needed a strategic location. They befriended Pakistan, helped Zia Ul Haq overthrow the democratic govt and put Zia Ul Haq in power. Funded Taliban (which in Persian means "seekers" or students in this case). Basically it was a students group that was causing agitation against Russia. So, Taliban got guns and funds so they started to uprise against Russian. Russia's grip on Afghanisatan weakened overtime. Taliban got stronger and started to rule Afghanistan with hardcore fundamentalism. Zia was not needed anymore, so he get killed in a plane crash. Now Taliban are strong so guess what, US attacks Afghanistan again. This time to get rid of Taliban.
You see, the circle goes on and on. First they make money planting a virus and then they make money removing it. While they do that, they are planting it in a region next to the original one.
Benefit to US: Higher gas prices. Arms industry flourishes. Other nations weaken. US stays on top. People's attention stays diverted from other issues.
As much as I feel terrible for people who lost their lives in 9/11 and I admire the cops and firefighters who did an extremely tough job, you would have a hard time winning any sympathy for US on a political level. As you sow, so shall you reap. I truly believe US doesn't mind the trouble though. More turmoil there is, more it benefits US.