Originally Posted by sub zero

Well I might be able to chime in, especially depending on which ex girlfriend, some might say I am the anti christ...
In all seriousness though I think it will happen economicallly. You will have the formation of a world government, something like the United Nations but with more concrete power. Once they are stabalized they will begin to consolidate power by offering to solve several of the world's problems, specifically hunger and poverty. How can they solve that you may ask, be alotting everyone in the world a specific amount of currency to buy neccesary items. Well how can they grant different currency world wide, by making one world wide currency. After this occurs we have to keep track of who spends how much, how else to do that than to create a world ID. Of course no one gets anything for free so to get access to this money you have to be in a nation that will accept to give up its currency for the world currency. Any nations that hold out will be seen as bad and an enemy of the world.
With sanctions those last nations will eventually give up and join the world nation with their world currency. Some years for sake of convience all money will become electronic and eventually be offered as a credit card or even a computer chip installed on your hand.
I know kinda wierd but this really sounds like the most plausible to me at least.