Actually many took a side of "Neutral" at the start of WWII, including the United States. The US didn't declare war until 3 years after WWII started. That is also why there was such a reaction to Pearl Harbor was it was a "sneak attack" as there was no war declared between countries involved.
I'm with all of the above, attacking without a declaration moves you to evil, and have both a declaration and threaten war. I don't know if there is this option since I dont have Galciv (Yet the way things are sounding

) but also have an option to tell allies to make peace with others. So you don't get the Civ3 problem of making peace, then an ally who is still at war with them drags you back into it.