http://forums.civfanatics.com/showthread.php?t=142181
You just gotta bribe the hell out of them...
If you're the tech leader in the game, you'll have plenty of ammo to spew out for a diplo win at the end...
Aim to get only the biggest voters that are friendly with your allies...
DO NOT trade with anyone the AI can't stand... If you do, cut relations with the weaker smaller civs before approaching to bribe the bigger ones...
Religion is a MUST if you want to secure a diplo win... You have to make sure they're your religion and stay that way...
Resources / military joint action will almost grant you a good friend over time good enough for some votes...
However, do not ever expect the 2nd place civ to vote for you... ALWAYS pick them as the enemy, and make sure they have less friends than you...
By the end, you should either war them before they war you to either gain large pop cities or like people say, nuke them...
War does win diplo in real life... Diplo is not determined by good faith, it's always the strength of your army that determines what others treat you as... So as far as it being broken? I doubt it... Nuking the planet is a bit far fetched, but how can you put nukes in the game and still be realistic?