Currently, all AI can really do is war each other, and it determines who to war off of the relative power of a civilization. For example, I am playing as the Romans in the GEM 30 Preset Civ, and Alexander and I have the two strongest armies, he is sending his into Arabia, conquering the near to middle east (sound familiar?) and I am sending my armies into Europe and Prussia. I used Alex for my Trade Caravans to fund my armies, and his bright yellow smile indicated he didn't mind at all.
In this game there was a 4,000 year stalemate between Spain and Portugal which resulted in a massive arms buildup. The two desperately wanted to declare war on each other, but couldn't muster a strong enough force (relative power) to accomplish the task as they both had the same agenda.
After I killed both Spain and Portugal, my armies were a bit weak, and Alexander then declared on me, despite our 6,000 years of peace, prosperity, and success in both fronts.
One might say that this could be considered a 'clever plan' by the AI.
No, it wasn't. They always react the same way. After I lost over half of my army in a costly assault for the last city in my way, I glanced at my power relative to Alexanders, and proceeded to move my army next to his territory. I knew it was coming.
Even if I conceited that it was a clever plan, the adjective clever would not apply as he had his armies near India at the time. Thanks for the free cities Alex, you really are a good team mate.
I quickly claimed his most precious cities before he would agree to a cease-fire (also heavily based on a Civ's power) so I could finally concentrate on building up my newly conquered cities.
Now what I propose is an addition to Advanced Diplomacy. Something along the lines of an option to "Agree to Corroborate Against 'x'".
The way it would work is each Civ can choose 1 other Civ to create a "mini-team" against another Civilization. There are a few ways you could do this. I think the simplest and best would be each Civ can only have a single Corroboration Agreement at a time, that way you won't find yourself in a position where you were asked to corroborate, and agreed, then you were either asked again by someone else, or started your own Corroboration with another Civ after the fact.
If there was such a system in ROM:AND, the previous two scenarios would have played out accordingly:
Firstly, Spain and Portugal could agree to corroborate against... Well... Who cares, anyone else besides each other. That would mean the arms buildup between the two never would have taken place, and both countries would be free to either set their eyes on their target, or any other Civ besides themselves.
Next, when I built my army and started to determine which cardinal direction was a good one to 'point' in, I noticed that everyone west of me was weak, and Alex had the second strongest army, closely following my own. The choice would be clear, corroborate with Alex, probably against Germany as they were the 3rd strongest, then proceed to massacre.
(Mental note, remove Portugal at the start of my next game so Spain will try a different strategy, as 1 city and 1000+ Javelineer's doesn't seem to cut it)
Also, keep up on those speed tweaks. Those are probably the only thing standing in between ROM:AND and perfection.
in each city after 3, or something like that.
Old ppl like me need detailed instructions sometimes. 
