I have been playing a LAN game with (I believe) 15 civs, 13 of which are AI. "Require Complete Kills" is on, but no other applicable options have been changed.

Roughly 25 turns ago Russia was finally destroyed, though their last city had fallen at least 50 turns prior to that. Now, the Aztecs have appeared, with Peter as their leader. I am assuming that these Aztecs are a colony split off from the Khmer, as they are a vassal state of the latter. The problem is that Peter is still at war with the same Civs that he was when destroyed (which was almost all of them), so now Khmer is at war with the same parties. Is this how it's supposed to work? Is this a bug?

I don't host the saves on my computer, but could come up with one if required. I really just want to know if this is a common occurrence. I saw this bug report thread:
http://forums.civfanatics.com/showthread.php?t=234301
but it doesn't sound like exactly the same issue.

Thanks for any help.

Oh, also: my captured Russian cities are now under the influence of Aztec culture and upset over being kept from their motherland.

Welcome to CFC :dance:[party] and
this is a known bug, install Bhruic's unofficial patch to patch this :)

Thank you, that sorted it out.