AxeZ, your examples are more emotional than reasonable. No monetary union is sustainable without some instrument which balances the economies of individual regions. It may be massive economical migration like in the US, for example, but in the European conditions there it is usually a fiscal transfer from the more developed regions to the less devoleped ones. In Czechoslovakia, Czech countries massively subsidized Slovak (and before the war also Ruthenian) economy, Slovakia was parodoxically the only region within Eastern Bloc which profited economically on the communist era, but no Czech politician would mind to use that card against Slovakia. And by the way, do you really think that Serbia was less developed than Kosovo?