Despite the treaty and the largely peaceful era that followed, the strategic position of the Bulgarian Empire remained difficult. The country was surrounded by aggressive neighboursthe Magyars to the north-west, the Pechenegs and the growing power of Kievan Rus' to the north-east, and the Byzantine Empire to the south, which proved to be an unreliable neighbour. Bulgaria suffered several devastating Magyar raids between 934 and 965. The growing insecurity, as well as expanding influence of the landed nobility and the higher clergy at the expense of the personal privileges of the peasantry, led to the emergence of Bogomilism, a dualistic heretic sect that in the subsequent centuries spread to the Byzantine Empire, northern Italy and southern France (cf. Cathars). To the south, the Byzantine Empire reversed the course of the Byzantine–Arab wars against the declining Abbasid Caliphate and in 965 discontinued the payment of the tribute, leading to sharp deterioration in their relations. In 968 the Byzantines incited Kievan Rus' to invade Bulgaria. In two years the Kievan Prince Svyatoslav I defeated the Bulgarian army, captured Preslav and established his capital at the important Bulgarian city of Preslavets (meaning "Little Preslav"). In this desperate situation the aging PeterI abdicated, leaving the crown to his son Boris II (r.969–971), who had little choice but to cooperate with Svyatoslav. The unexpected success of the Rus' campaigns led to a confrontation with the Byzantine Empire. The Byzantine Emperor John I Tzimiskes eventually defeated Svyatoslav's forces and compelled him to leave the Balkans in 971. In the course of their campaign the Byzantines seized Preslav and detained BorisII. Initially JohnI Tzimiskes presented himself as a liberator but BorisII was promptly forced to ritually abdicate in Constantinople. Although at the time the Byzantines controlled only the eastern regions of the country, Bulgaria was proclaimed a Byzantine province.