Well, this certainly would explain some strange things in my last campaign, where after a few years no AI took over any territory despite massive armies. More to the point, I guess they didn't take any after I started using assassins. I, um, always give them a second chance if they, erm, are not sure what to do the first time. So, basically, due to the amount of spies and diplomats that have been sent my way, I was essentially reloading almost every turn - and nobody took over any territory as a result.
It actually would have been cool to have Carthage around for so long for once, if only I hadn't wiped them out at the start...