The wars Hostile_encounter were dominated Control by land campaigns Military_operation in Hungary , including Transylvania ( today in Romania ) and Vojvodina ( today in Serbia ) , Croatia and central Serbia .

The Entente promised Commitment the region of Transylvania ( which was part of Austria-Hungary ) in return for Romanian support Supporting .

The Romanian Army invaded Attack Transylvania and had initial successes , but was forced to stop Process_end and was pushed Motion back by the Germans and Austro-Hungarians when Bulgaria attacked Attack them in the south .

Later , during the 10th century , the Hungarians overran the Bulgarian dukes in what is now Transylvania and conquered Conquering the eastern parts of the Pannonian Plain .

The Bohemians made Manufacturing offers to the Duke of Savoy , Elector of Saxony ( the preferred candidate ) and even to the Prince of Transylvania .