Led by a Varangian dynasty, the Kievan Rus' controlled the routes connecting Northern Europe to Byzantium and to the Orient (for example: the Volga trade route). The Kievan state began with the rule (882–912) of Prince Oleg, who extended his control from Novgorod southwards along the Dnieper river valley in order to protect trade from Khazar incursions from the east and moved his capital to the more strategic Kiev. Sviatoslav I (died 972) achieved the first major expansion of Kievan Rus' territorial control, fighting a war of conquest against the Khazar Empire and inflicting a serious blow on Bulgaria. A Rus' attack (967 or 968), instigated by the Byzantines, led to the collapse of the Bulgarian state and the occupation of the east of the country by the Rus'. An ensuing direct military confrontation between the Rus' and Byzantium (970-971) ended with a Byzantine victory (971). The Rus' withdrew and the Byzantine Empire incorporated eastern Bulgaria. Both before and after their conversion to Christianity (conventionally dated 988 under Vladimir I of Kiev—known as Vladimir the Great), the Rus' also embarked on predatory military campaigns against the Byzantine Empire, some of which resulted in trade treaties. The importance of Russo-Byzantine relations to Constantinople was highlighted by the fact that Vladimir I of Kiev, son of Svyatoslav I, became the only foreigner to marry (989) a Byzantine princess of the Macedonian dynasty (which ruled the Eastern Roman Empire from 867 to 1056), a singular honour sought in vain by many other rulers.