Here's my idea for a diplomacy implementation - alliances.

If you want to forge an "alliance" with someone, you both sign a treaty.... and deposit money in a "galactic bank" of some sorts (future version of IMF or similar - GMF - Galactic Monetary Fund?).

I'm sure we could get advanced on how much money you put in, but for simplicity's sake lets say 50/50. Perhaps there's various factors involved in who puts in more - and perhaps there's some diplomacy skills that lets you negotiate better deals. I'm imagining a popup dialog with sliders and offers etc etc.

You now have a "treaty" with that race, and you are allies. You can't attack unless you break the treaty.

While you have this alliance, you both earn interest on the amount of money deposited (another reason for keeping the treaty). The GMF invests it in menswear or oppressing developing planets.. just like in real life.

If you break the treaty and attack your ally, they get all the money that was deposited.

I'd imagine all this diplomacy should be tied into some kind of "reputation" system, (breaking a treaty lowers your rep) but that's a topic for another post.

Thoughts?