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MotormouthYes the whole UK-GB-England thing is very confusing to us on this side  of the pond.  I would guess to say that the average American does not  know the difference between the three.  Ie if  England-Wales-Scotland-Northern Ireland are one country, why do they  have separate world cup teams.  It would be like the US having 50  different teams.
Exactly because we are unique nations  with different racial make ups. The Scottish, Welsh and Irish are  primarily from Celtic ancestry while the English are Anglo-Saxon. They  each speak different languages though English is now the common  language. They have different traditions and yet we have a common  history going back hundreds of years. 
Yes, Wales isn't directly  represented on the Union Flag and yes the term Great Britain is used for  the Olympics when it is still technically the United Kingdom of Great  Britain and Northern Ireland.
We have seperate teams because we  like competing against each other. We feel passionately about our  difference as well as our commonality with our Westminster Parliament, armed  forces and governance systems. The 50 U.S. states I'd argue are not quite  different enough either in their racial make up, traditions or heritage  to warrant similar passions or interstate rivalries. I guess it would have been like having four  separate unions made up of French, Dutch, English and Spanish settlers  all living as separate states in northern America for a hundred years before uniting into a  four 'state' United States. Does that make more sense?