Settings: There is a far away civ who has a strong infrastructure and discovers techs faster than you. This happened in a recent game of mine on Emperor level, random settings who gave an archipelago map. I was the Babylonians and the rival civ was America. What do you do in such a situation? They are far away, therefore you will need a lot of time to get to their territory, by the time you get there they may have better units etc.
What I did: I contact the Americans and ask to buy technology. They have free artistry, scientific method, communism and replaceable parts. I buy RP, I don't give them any cash but agree to pay 120 gold per turn. Then I negotiate peace. Since their forces outnumber mine they ask for "something" in order to agree to a peace treaty. I let negotiations fail. Now I am at war and I don't have to pay the 120 per turn.
I contact all the other civs and ask them to ally with me against America. They ask for money, or a resourse or a technology. I give them whatever they want. Now America is at war with everybody. That's all. Essentially I got RP for nothing and have my rival at war with all the others. I continue with Democracy and have no unrest because my forces are within my borbers and no battles ever took place. America is far away and too busy fighting the others she has borders with, to send an expeditionary force to invade me. The 20 turns pass quickly, I cancel my alliances and sign a peace treaty with America. The others, or most of the others are still at war
Poor America doesn't research as fast anymore. My relations with the other civs are good (I kept my treaty with them and "fought against" a common enemy)
-