Nomad Avar horde, which migrated to the Balkan region from Asia, soonly was included in the diplomatic system under the supremacy of Constantinople. After using territorial claims nomads on Romei lands, a short form of the institution of the supreme ruler and a small number of Avars, Roman Emperor Justinian I (527-565) signed the federative agreement with nomads. During the alliance, Avars tried to develop their independent political course. Such circumstance contradicted Eastern Rome’s interests and, in perspective, created a direct threat to the Empire. Using centuries of weakening the Byzantium on the Danube border, nomads started a series of raids against Empire allies and broke the deal with Constantinople. The diplomatic corps of nomads focused on disinforming the autocrat. As a result, it caused deterioration in relations between sides in the last years of rule of Justinian I and finally to a protracted military confrontation after the death of the Emperor, which lasted with breaks to the first third of VII cent. The main thesis of the article is the Avar-Romei political relations, which topic is considered primarily in the context of the wars. At the same time, the only basileus who succeeded in managing the long-term alliance with the future enemy of the Empire was Justinian the Great. In our opinion, the consideration of Avar-Romei political relations in this period illustrates, on the one hand, the specifics of the attitude of ‘Latin’ Byzantium to folks whose military potential it wanted to use. On the other hand, the peculiarities of the formation of another ‘steppe empire’, which by the way, turned out to be more stable in ethnic and political aspects than the Huns. Based on the messages of Romei historians in the second half of VI cent., the article recreates the terms and the precedents of concluding and further observance by the parties of the Avar-Byzantium alliance during the final period of Justinian the Great rule. The author tried to chronologically recreate the picture of the initial step of Avar-Romei relations that primarily evolved in mutually beneficial coexistence. This was primarily caused both by low numbers of Avars and insufficient formation nomads’ elites, as well as the political experience of Justinian the First. The focus is on the relations between nomad folks and Empire federates, such as Alans, Antes, and Gepids. Against the background of military-political connections of Avars with their neighbors, their first initial steps are noticeable. Analyzed factors that promoted Avars’ initial transition under Rome’s supremacy and the slow creation of their own policy course by Avar Khagan Bayan.