really cool way to get money

I have found a interesting thing that AI's do. Get into a war with a weaker civ, then start pummeling their defenses but don't take over all their planets. They should start bugging you for peace treaties. Reject them for a year or two, then accept the deal, but say to them that you want 100 for as many months as you want. The proposal will turn green when they will accept. I've gotten extreme income of about 700 later in the game with this. Try it out .