Which was not a response to the September 11 terrorist attacks on the United States? Iraq denounced the events and disassociated itself from al-Qaeda. World leaders pledged support to the United States during its recovery. Citizens all over the country came together to support each other and the president. The president requested and received congressional authorization for the use of military force.
I believe it was the first one, because believe it or not much worse thing shave happened in other countries and has never caused something that radical. That would be like all the countries going against one, which will most likely never happen because of all the allegiances and past grudges. You could check a news website like CNN or your local news station and they are bound to have something on it though. The anniversary was just over a month ago, so some information should still be newly available.