Iorga's writings insisted on the importance of Byzantine Greek and Levantine influences in the two countries after the fall of Constantinople: his notion of "Byzantium after Byzantium" postulated that the cultural forms produced by the Byzantine Empire had been preserved by the Principalities under Ottoman suzerainty (roughly, between the 16th and 18th centuries). Additionally, the Romanian scholar described the Ottoman Empire itself as the inheritor of Byzantine government, legal culture and civilization, up to the Age of Revolution. However, the "Geschichte des Osmanischen Reiches" postulated that the Ottoman decline was irreversible, citing uncompromising Islam as one of the causes, and playing down the cohesive action of Ottomanism.