With a POD no earlier than 1900, is it possible to create an a pan-Eastern European alliance, comprising Romania, Bulgaria, Czechoslovakia, Yugoslavia, Hungary, and possibly Greece and have it play a major part in at least one world war?
Maybe a different Austria-Hungary could lead to this. With a POD in 1900 there might be enough time to do some good reforms. Perhaps some kind of relaxation of Magyarization and more democratic reforms in Hungary. Then as the Habsburgs collapse the resulting nations are friendlier to each other and some kind of economic organization is put into place.