Was gonna reply w/ something like this but we did have a few... Germans invaded near the statue of liberty and blew shit up (ww1).... and Pearl Harbor...those were technically acts of war, but amounts to the same, and the sinking of the Luscitania...

But, for the most part America has been safe before and after the one isolated event of 9/11 and there's no proof that anything we've done since has made us safer (likely it's had the opposite effect by stirring up animosity).