OK I'm not basing this on any facts- but then again, when do I ever
But it seems to me that the size of your military determines if you win or lose. Even if you play peaceful you need a large military to keep the ai from bullying you. And for obvious reasons you need a large military to take over other civs. The size of your military also determines your effectiveness in diplomacy.
I'm thinking they use a system similar to civ2 (or was it smac?). Where they add up attack and defense values. Even when I upgraded all my spearman to infantry (I had a huge tech lead
- and I had already conquered my entire continent- I use offensive units for defense anyways), the ai changed their attitude towards me. This shows they value the accumulated defense value of all your units.
The same goes with offensive units. Uprgrading all my horsemand and knights to calvary also changed the ai attitude. It does not matter if they have an embassy or not I believe.
This may be common knowlege, but I know some are struggling with the game. In civ2 I got by with minimal defense, and very little offense until I got howitzers. That is not possible in this game.
My advice? keep your units upgraded and build more. The ai will give you the respect you deserve. My only loss came up when the ai did not respect me because of my small military and ganged up on me and wiped me out.