 Complete the following phrase:  Between 850 and 1100, the Empire developed a mixed relationship with the new state of the Kievan Rus, which had emerged to the north across the Black Sea. This relationship had long-lasting repercussions in the history of the East Slavs, and the Empire quickly became the main trading and cultural partner for Kiev. The Rus launched their first attack against Constantinople in 860, pillaging the suburbs of the city. In 941, 