Perceptions of "what is a war?" are weird.

I once had a law student tell me that the invasion of Iraq was not a war. This left me scratching my head. I then asked him a few questions, such as, "so the US military fighting against the Iraqi military is not a war?" Finally, he explained that it was not a declared war. Once that was established, I had to ask what significance that had to the original topic that we were discussing. He couldn't think of one. Neither could I. But it was weird that he would suddenly rise up on this point that was so insignificant within the context of the discussion. It is not an uncommon reaction - I've seen and heard it several times in other situations. I've never understood why people insist upon declaring open hostilities involving military forces to not be wars.