Nagasaki and Hiroshima: Terrorism?

I know I risk being labeled the ultimate lefty for posting such thought... but how necessary was the use of atomic weapons at the end of World War II?
How necessary was it to drop TWO bombs?

We'd defeated Germany... and it didn't look like Japan had the upperhand by any means, nor did surrender look far off.

And considering that the intended victims of the atom bombs were civilians, and the purpose was not strategic, but to instill fear... why weren't and aren't these means considered terrorism any less than the attacks of 9/11?

The comments are open for discussion on the matter.