AI Intelligence levels.

That table is in the manual. It lays out the negatives or bonuses the AI gets at each level plus the algorithms they use.

The Wiki article is of some help, https://www.galciv.wikia.com/wiki/Difficulty_level. Basically the difficulty level and the corresponding AI level are listed, like Cakewalk = Fool and Tough = Intelligent and Suicidal = Ultimate. In the case where all AI intelligence levels are set the same then that tells you the difficulty level. The only real difference comes when you set different AI's to different Intelligence levels. In this case Difficulty is in some way an "average" of your opponents intelligence. How this average is figured is unknown. Way back in the day it used to be determined by the highest AI intelligence so you could play one Ultimate and 8 Fool's and still count as Suicidal but that hasn't been true for quite some time.

[edit]  One final point. If you change the starting relations from unknown then in general your reported difficulty will be less as well. In my first Suicidal game, I set initial relations to "friendly" so that hopefully I wouldn't be so quick to be attacked. The end result was that the game reported as Obscene even though all AI intelligence's were set to Ultimate. Plus it didn't really seem to keep them from attacking me anyway. [/edit]

I actually wonder if this is still true Mumble, at least in the current version of DA. The ZYW's that i have been doing, the last 40 or so anyway, have been one AI on suicidal and relations set to friendly. As you can see in Centurion Neilo's profile, my games were still reported as suicidal.

Perhaps it was changed again as i do know that it once was as you described, and i hadn't really thought of it again till i read your post and it hit me, my games were suicidal.

Thanks for finding the right wiki page Mumble . The link on the databanks page seems to be broken and even searching within Wikipedia I couldn't seem to get to the right page.

Okay, thanks alot, this cleared up things quite well. So I should play on Intelligent then to get a nice challenge while not getting overwhelmed instantly?

It sounds like you're just starting out. My advice is not to get too hung up on difficulty level. Just start somewhere and if it's too much don't be afraid to crank it down or up as needed. You'll find where you want to start out soon enough. You should be able to keep up with the AI's colony rush.

The thing is you'll start out and the lower levels can be very easy as the AI hardly does anything but the levels are not all that "smooth". There's a couple of different points where you'll increase the difficulty by a notch and be suddenly surprised at how much more difficult the AI is. IIRC going to tough was one such level. Another is going from obscene to suicidal, that can be a huge jump.