Hi! I am playing an emperor aggressive AI game, where I am blocked from the other civilizations by Shaka, I share his religion, and he is friendly to me. I am going for a cultural victory, and I can cope with the other AIs because I hardly spend on military. Everything is fine except for the fact that I am vulnerable. I have just got feudalism, and thought I could voluntarily be his vassal, so that I am safer, until there are defensive pacts. BUT it's not possible . Is there any trick or this feature is just simply not implemented?