During the period from 1400 to 1600 A.D., Anatolia and the Caucasus witness a shift from the earlier fragmentation (1000–1400 A.D.) to increased unification. While the Caucasian region remains independent during the earlier half of this period and then becomes a frontier zone between the Ottoman and Safavid empires, Anatolia is tied to Ottoman imperial capitals in the Balkan peninsula, Edirne (Adrianople) and Istanbul (Constantinople). With the great Ottoman expansion in the sixteenth century, Anatolia becomes part of a world empire. Earlier heterogeneity gives way to a uniquely Ottoman synthesis of different artistic traditions.