You forgot to mention about the United Planets. One stratigy is to vote for the 20% humanitarian tax, then goad civs to go to war with each other, while you're keeping on top with economy. Eventilly all the civs will start to get broke and can't do anything. Then they will start surrendering to each other, and if you're lucky, soon all races will surrender to you.
Its also cool when they get like -5000, go broke, and surrender to another friedler nation. Its so easy :D
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 :) .
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