acts of terror can perhaps be well qualified by numbers killed:
deaths in Viet Nam amounted to around 3 million, numbers killed in illegal bombing of Cambodia about 500,000........these being direct acts of us terror.
of course if you take into account indirect us sponsorship of terrorist states and cia overseas operations, then its pretty clear that there is no question that the us has been (and is) the most prolific terrorist nation on earth.
of course if you have valid evidence to suggest that either Iran or Syria has also had direct involvement in sending upwards of 5 million people to their deaths over the last 50 years say, then obviously i am quite wrong!