Grand Prince Géza died in 997. Stephen convoked an assembly at Esztergom where his supporters declared him grand prince. Initially, he only controlled the northwestern regions of the Carpathian Basin; the rest of the territory was still dominated by tribal chieftains. Stephen's ascension to the throne was in line with the principle of primogeniture, which prescribed that a father was succeeded by his son. On the other hand, it contradicted the traditional idea of seniority, according to which Géza should have been succeeded by the most senior member of the Árpád dynasty, which was Koppány at that time. Koppány, who held the title Duke of Somogy, had for many years administered the regions of Transdanubia south of Lake Balaton.