Sviatoslav's brief sojourn into the south awakened in him the desire to conquer these fertile and rich lands. In this intention he was apparently encouraged by the former Byzantine envoy, Kalokyros, who coveted the imperial crown for himself. Thus, after defeating the Pechenegs, he set up viceroys to rule Russia in his absence and turned his sights southward again.

In summer 969, Sviatoslav returned to Bulgaria in force, accompanied by allied Pecheneg and Magyar contingents. In his absence, Pereyaslavets had been recovered by Boris II; the Bulgarian defenders put up a determined fight, but Sviatoslav stormed the city. Thereafter Boris and Roman capitulated, and the Rus' rapidly established control over eastern and northern Bulgaria, placing garrisons in Dorostolon and the Bulgarian capital of Preslav. There Boris continued to reside and exercise nominal authority as Sviatoslav's vassal. In reality he was little more than a figurehead, retained in order to lessen Bulgarian resentment at and reaction to the Rus' presence. Sviatoslav appears to have been successful in enlisting Bulgarian support. Bulgarian soldiers joined his army in considerable numbers, tempted partly by the prospects of booty, but also enticed by Sviatoslav's anti-Byzantine designs and probably mollified by a shared Slavic heritage. The Rus' ruler himself was careful not to alienate his new subjects: he forbade his army from looting the countryside or plundering cities that surrendered peacefully.

Thus Nikephoros' scheme had backfired: Instead of a weak Bulgaria, a new and warlike nation had been established at the Empire's northern border, and Sviatoslav showed every intention of continuing his advance south into Byzantium.