Everything I am coming up with is a game modification requiring GM intervention.
I've seen online games with built in 'niceness' incentives. In SC it would be things like a top 100's for: Friendliest Country, Most Aggressive Country, Fastest Growth, Most aid/Most helpful, Most revered, Most Hated... etc.
Hey, in the past, it's had me offering disaster relief for no other reason than climbing in the ranks in that ranking system.
Maybe there should be a Friends/Enemies list for our countries and then certain things on the list are scored for the community to compete.
I have seen the concept work.
I imagine a system where there are multiple ranking boards, one for presidents and one for countries one for the military etc.