Should the U.S. be brought before war-crimes tribunal for WWII?

I am an american living abroad in japan. Sometimes when me and my japanese friends get drunk we talk about WW2. It use to be a little uncomfortable for each of us but we highly respect each others opinions in intelligent debate. My friend thinks that the U.S. should be brought to a war-crimes tribunal for the dropping of the bombs in Hiroshima and Nagasaki. I brought up Pearl Harbor of course and she said that the Japanese attacked a military installation, not a city populated with plain ol civilians. I said it was a sneak attack. She says that the U.S. knew it was going to happen and wanted a prelude to test its bombs and to get into the war. From there I have read some books from www.disinfo.com and I am starting to have a different opinion about WWII but I feel guilty because for years I was taught that things occurred a totally different way. Your take?