Negative modifiers for defending yourself?

[Green_Power]

I had three to six AI's declaring war at me simultanously atleast three times until modern age. Just because I destroyed a crazy forward settled German city and one close by city state during medieval age. That never happened in G&K to such an extreme.

It was like that in G&K already. You can't just take a city-state just because you feel like to and expect that others don't react to that. I did the same in G&K. Took a nearby city-state just because. I was never trusted by anybody again. Can't blame them can you?

 

[PhilBowles]

I've never gotten a diplomatic hit from not joining in a war when someone asked me (unless I promised to in 10 turns and later reneged). They don't seem to care if you join them and do absolutely nothing to attack the target either.

They don't, but you're more likely to get the "fought against a common enemy" bonus if you do actually fight.