Not long ago I read of a Cuban American who hijacked a small plane (which I belive crashed).

You can look to Oklahoma City for a major bombing on U.S. territory not committed by an Arab or Muslim

You can look to the hundreds of bomb threats made daily which I am certain are not all made by Arabs or Muslims.

You can look to the acts of terrorists in Ireland and England.

You can look to "American" groups who commit attacks designed to terrorize others (for example the KKK).

And depending on your political bent you might even accuse certain US agencies of commiting terrorism.