When the Hungarians start attacking Transylvania, the Transylvanian Romanian boyars decid to crown one of them (most probably Gelou) as Voivode and he succesfully stops the Hungarian expansion. After that, he is recognised as ruler by the Wallachian and Moldavian boyars and, to solidify his rule, he converts to Catholicism to be crowned by the Pope as "King of the Rumanians". Take into account the fact that Hungary hasn't converted to Catholicism yet so Romanians could be seen as defenders of Christianity in the face of the pagans, so the rest of Europe could turn it's attention to weaken and convert Hungary. I would love to write a TL on this POD in the future.