What hapoend

On this day terist made an attempt to hijack a air plane and crash it in to the World Trade Center and took both the towers down. People were in great fear people wonder are all the planes getting hijacked and are we going to get in all of America what going on. I want to know what would Usama get out of this? I think Usama wanted to scare us off to leave their country but I dont think thats it I know that Usama was in the army with americans and he went to war with his own kind and he didnt want that so he betraid us and did this attack on us.