Primarily through trade, but also through occasional careful use of force (such as the sack and destruction of Comacchio in the 930s), Venice by the year 1000 had extended its area of influence across the Northern end of the Adriatic Sea, encompassing the Istrian penninsula on the opposite shore. Thus, the Bay of Venice became a safe haven for pervasive Venetian shipping.

The mid part of the Adriatic, however, remained a difficult and unprotected no-man's-land for Venetian ships. South of Istria, along the Dalmatia coast, Slavic invaders from the upper Balkans had seized control of the area where the Narenta [Neretva] River enters the Adriatic, as well as the islands such as Lesina, Curzola and Lagosta that lay in the river's delta and protected its mouth. From that stronghold the Slavs launched incessant pirate raids on Venetian merchant ships that attempted to run their gauntlet and reach the Mediterranean. Sometimes the Slavs were joined by marauding vessels from former Roman cities of the upper Dalmatia coast, such as Zara and Spalato; at other times the Slavs preyed on those other Dalmatians as well.

After several unsuccessful, and sometimes disastrous, military attacks on the Dalmatian pirates from the late 9th to the mid-10th century, the Venetian merchants expediently arranged to simply pay the Dalmatians an annual tribute for safe passage of their Venetian ships.

From the time of his election as Doge in 991, Doge Pietro II Orseolo wove a net of diplomacy through the Northern Adriatic and upper coast of Dalmatia as a foundation for the total extinction of the Dalmatian pirates and Venice's first major territorial expansion.