I'm sure few will agree with this concept but, I believe the healthiest future for the Earth doesn't include countries and nations. Yeah, you guessed it, I'm a big supporter or the United Nations.
The death of all countries and the combined world society and economy wouldn't solve all of our problems, I know this.
National pride, also known as ignorance about anything outside your own country, would be less prominent. Cultural pockets would continue to exist, I know, but if the all out reason to work hard was for Earth instead of America or some other pathetic country, I think there would be less breeding of idiots.
This isn't a soon to be seen existence. The European Union is one of the starting points. Countries working together for mutual success.