From level "emperor" on I have regurarly a problem to beat the AI when a running up Civ has developped the United Nations wonder. Normally he has so much money that he can afford it to maintain the CS with gold up to the election. Is there a way to beat this, once UN has been builded or do you have to look ahead ?
Buy up a few civs and then declare war before they are repurchased by the AI.
Also, figure out what VC you want by turn 100 or so. Work on attaining it before turn 350.
Globalization is very high on the tech tree, and the fastest way to get there is to sign research agreements. A good way to keep a runaway civ from signing non-stop research agreements is to deprive their would-be partners of gold. You can do this by signing your own research agreements with the lesser civs, selling them your extra copies of luxury goods (or only copies if you've got the happiness to spare), open borders, and any strategic resources you don't use.
Also attacking and destroying the runaway civ might be a good idea but obviously you have to plan ahead because if they build the UN then there is not enough time to attack.
Has anyone testet what happens if you capture the city that built the UN? Do you get the extra votes for yourself? If it's a non capital and you raze it, would it stop the vote?
Buy as many city states as you can from them, sell resources to other civs if you need, Declare war on him and nuke every high-gold tile he has; or just nukeMissile all his cities into oblivion
You can also swallow enough city states that there are not enough votes left for the vote.
Conversely.. if you free city states someone else swallowed, their votes cannot be bought...
Of course, if they had the tech for the UN, the tech for the spaceship is not far behind so unless you are buying time in an otherwise close race... I find rebooting stops the AI dead in its tracks.