If the rest of the world joined the USA... what would change?

[Mehmentum]

Infrastructure: Members of third world regions would strongly support infrastructure building projects in less developed areas.  Members of first world countries would strongly oppose such a measure.  The most distinct party divide would almost certainly be around this issue.  With an almost entirely first world v. third world divide in voting behavior.

Social Issues: Multiply what we have in the USA by about a million.  Consider that as a part of this new United States of the World there would be both the most liberal European countries and the most extreme islamic states, where gays are still stoned to death.

Third Parties: I wouldbe surprised if a two party system could succesfully satisfy the entire diversity of the world.

I find it more interesting to think about how a world government would be set up.  I think the U.S. is actually a good model.  All of the states thought of themselves as seperate entities when the constitution was written, which is why we have a federal system.  Any world government would need to start out like the U.S. did, with a lot of power delegated to individual nations, but with not making the central government useless like the Articles of Confederation.