I thought I saw in the 3.13 changelist something about AIs only capitulating to the civ that caused them the most damage. So, I was waging war against Wang Kon and he was down to his last 2 cities. I didn't really want him as a vassal, so I was preparing to finish him off, when suddenly my good buddy (he was at "friendly") Frederick DOWs on me. Then there's a message "Wang Kon has become a vassal of Frederick". I was like WTF? So I reloaded the most recent autosave and sure enough Wang Kon was perfect happy to accept vassaldom if I offered it. So why didn't he offer to capitultate to me? It seems like there's several issues here: 1) Is a civ supposed to offer themselves to another civ who they are not at war with, and thereby automatically bring that other civ into the war? 2) If the answer to #1 is yes, does the AI consider whether they want to DOW before accepting the vassal? I don't know if it's really a bug, but it seems fishy to me.