King Demetrius Zvonimir of Croatia's wife, Helen, was Ladislaus's sister. After the death of Zvonimir and his successor, Stephen II, a conflict developed between factions of Croatian noblemen. At Helen's request, Ladislaus intervened in the conflict and invaded Croatia in 1091. The same year, he wrote to Oderizius, Abbot of Monte Cassino in Italy, about his invasion. Thomas the Archdeacon's chronicle describes how Ladislaus "occupied the entire land from the River Drava to the mountains called the Iron Alps without encountering opposition". However, his opponents crowned a local nobleman, Petar Svačić, as king. Svačić fought in the Gvozd Mountains, preventing the complete conquest of Croatia. Ladislaus appointed his nephew, Álmos, to administer the occupied territory. Around the same time, Ladislaus set up a separate diocese in Slavonia, with its see in Zagreb. The bishop of the new see became the suffragan to the archbishop of Esztergom in Hungary.