@nokmirt - The problem with anecdotes like "I don't think the AI made the right choice" it is not testable, furthermore, the human player on the receiving end have immense advantages, in superior use of units, conservation of damaged units, and the reload option. Based on the infoaddict analysis, the choice was a fair one. You had a large empire with a smaller military. That's a classic case of overstretch and another AI with that confirgration would definately be vulnerable. And AFAIK, the diplo AI is human blind when it is deciding who to attack.
Not saying you reloaded or anything, but it's not really useful in a discussion about the AI to introduce that sort of subjective anecdote.
Where did you get the information that warmonger hate is related to capturing cities because a other poster on this forum posted a big post that warmonger rate is only related to 2 things:
Did I say that? I said capturing city states count as wiping out a Civ, and that the old exploit of turning a defensive war into a world conquering spree without having to DoW yourself is no longer diplomatically free.
The .XML values doesn't provided a flat penalty for capturing cities that are not capital cities or a city state, but then again it doesn't have to. The AI looks at a bunch of other factors as well, some of which we don't know about. This isn't related to 'warmonger' penalty per se, but it's not uncommon previously friendly AI become guarded or denounce you when it looks like your pulling away. And it could be any number of factors under the hood. Like score differential growth, or simply owning tiles they want that you had recently captured, so envy of the vanquished civ's land transfers to you.
Thanks for finding the post citing the 1 free war thing. As I noted, I didn't doubt it's something they would do, but the post is only an observation. Though It seems like a sound observation.
That said, it is worth noting it was made in July 2011, so it was probably based on the April 2011 patch. There was another big patch in August. I do not think the diplomacy got a huge upgrade in August but they did add another modfier "We have traded recently" which is a positive relationship modifier if you've given the AI a good deal. This can include free gifts, discounting lux for gold prices, and taking less than what the AI is willing to give up during peace negotiations.