Darius's status was "Afraid", not "Guarded" or "Hostile". The mouse-over said "They fear our military might. I've never seen this before, even when I was completely dominating in terms of military might. In this instance, I was only the #4 military, and Darius certainly wasn't in last place. In fact, he had more points, more population, more units, everything. Maybe on Deity the AI doesn't know it has a significant advantage? All the games I've played, I've never seen that.