Well, first I simply believe that you should not force areas together against what the people want. People have a right to choose for themselves.
Secondly, I really do not think that you can compare Europe and USA that way. The European countries were created over a long, long time and ended up really different, while USA was colonized by white people over a relatively short time.
What that would mean in the long run is anybody's guess, but surely the history would be markedly different from that of Europe.