"Impractical" was probably the wrong word to use; the nation-state system is ingrained into the minds of the public, and undermining "national soveriegnty" is usually recoiled from. The EU seems to be the first experiment of replacing nation-states with a continental-type state, so we'll see what happens there. In my lifetime, I would not be surprised to see the international arena dominated by these continental-unions, I think that a world federal government is still too foriegn of a concept for many to accept.

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No man is an island...
Each man's death diminishes me,
Because I am involved in Mankind.
And therefore, never send to know
For whom the bell tolls;
It tolls for thee.
—John Donne