How Many Have to Die?

The Pentagon said today that the North Korean torpedo attack on a South Korean patrol boat, which killed 46 men and sank the boat, was not "an act of war."

Well, this is an interesting question. The sneak attack on Pearl Harbor in 1941, which killed over 2100 people, was presumably an act of war since the president the next day called it "a day that will live in infamy" and shortly thereafter congress declared war on Japan.

On the other hand, 46 dead is apparently not an act of war. I guess this mean that to qualify as an act of war you have to lose more than 46 but not some any as 2100.

So the question remains. What is an act of war? 200 dead? 500 dead? Depends on the circumstances?