In my current DA game (gigantic, abundant, max players, suicidal), I gained an Alliance with the Yor while they were at war with the Korath (easily the strongest empire, but cash poor).
I asked the Yor to make peace with Korath, and they said they'd love to, but that the Korath would not.
So, I bribed the Korath to make peace, they took the bribe and agreed, made peace, and then declared war again in the same turn! That left me either declaring war on the much stronger Korath or forfeiting the Alliance with the Yor!
Back in MOO2, there was a period (~10 turns?) where an AI would not violate/terminate an agreement. Apparently, there is no such thing in Gal Civ?
Delightfully sneaky, btw .... 