I'm currently playing a game on Tough as the Drengin, and the Yor declared war on me about 10-12 weeks ago, but they haven't attacked yet. I've seen one or two of their fleets, but they just sailed right past me and back into their own territory.
They are the third race that's at war with me currently and are right next door to me; they actually have two of my planets surrounded by planets of their own. Why would they declare war and then not attack? I currently have the lowest military rating out of all 7 races and am fighting with tiny ships against other tinys and the Arcean's small assault fighters.
On a related topic, I'm rather surprised that I've been holding my own and actually winning the war against the Iconians. I expected to lose pretty quickly when the Yor joined the Iconions and the Arceans in the we hate you, you evil Drengin bandwagon. Does the AI get any smarter than the setting on Tough? They should all be intelligent, right?