Among Shepard's theories is that the breakdown in Byzantine-Khazar relations and the shift in Byzantine foreign policy towards allying with the Pechenegs and the Rus against Khazaria was a result of the Khazar conversion to Judaism.
In addition to the early Rus', Pritsak's works focused on Eurasian nomads and steppe empires such as those created by the Bulgars, Khazars, Pechenegs, and Kipchaks.
The Pecheneg is named for the Pecheneg people, a warlike tribe of Turkic origin who lived in what later became steppes of Southern Russia and Ukraine.
Starting in the mid-10th century, the Tivertsi frequently carried on fights with the neighbouring Pechenegs and Cumans.
He was the first to publish many medieval Greek sources relating to Russian history (Byzantium and the Pechenegs, 1872).
In 1051 or 1052, Nikephoros Bryennios defeated a Pecheneg detachment near Lardea.
In 1087 he commanded the Byzantine right wing in the Battle of Dristra against the Pechenegs, and in 1090 he defeated a small force of 300 Pechenegs while leading the Archontopouloi tagma against them.