The word "Sclavini" was introduced by Byzantine chroniclers at the end of the VIth century.
It was used to designate the totality of territories occupied by the Sclavini which were located on the left bank of the Danube, hence in today's Wallachian lowlands. At that time, the Danube River with its system of fortresses was still a serious defensive border, which kept to some extent the pressure of the Sclavini masses.
In "The Miracles of St. Demetrius" (in the part composed between the end of the 6th century and 620), referring to the first attack of the Sclavini and Avars against Thessaloniki in 586 or 597, the Sclavini are mentioned:
Sclavinia was perceived as an independent Slavic principality, which was located outside its neighbouring countries. In the beginning, this neighbour was Byzantium, which had claims to the territories on both banks of the Danube. Of course, the control of the empire was more theoretical than real, as the advancing numerous masses of Sclavenian settlers drove out the garrisons and captured the former Eastern Roman fortresses and settlements. Later, upon the arrival of the Bulgarians of Asparukh, some type of union under contract occurred between them and the Slavs, who had already settled permanently. Khan Asparukh managed to impose his authority on the Sclaveni, and even displaced and resettled some of them so as to protect the most vulnerable and dangerous sections of the border. But the Slavs, although acting as federates in the newly created state of Danubian Bulgaria, continued to enjoy certain privileges and conserved their rule over their allotted land. It is no coincidence that when talking about the joint actions of Bulgarians and Slavs, some Byzantine chroniclers do not fail to mention that the army consisted not only of Bulgarian cavalry but also of allies recruited from the surrounding Sclavinia. This clarification shows that the tribes that the Bulgarians encountered on their arrival had enough power and strength to allow them to continue to rule independently and to have their own land for at least another century.
The last mention of this specific term in the Byzantine chronicles refers to 809-810, when Nikephoros Ist Genikos ordered to resettle all the Christians of the Byzantine themes in Sclavinia. In 811, the Bulgarians recruited fighters from the Sclavinii, closer to the capital Pliska, hence the allied tribes that entered the state union. Undoubtedly, when facing the decisive battle in the Varbitsa Pass against Emperor Nikephoros, Khan Krum summoned the Sclavini soldiers under his banner, from the territories around the "Inner Region". It is certain that those were the northerners, the seven Sclavenian tribes (which included the Timochanis, and most likely the Moravians, the Praedenecentis, etc.). It is not excluded that additional militias were incorporated in the army of Khan Krum, from the Slavs closer to Bulgaria, located in today's Macedonia. After the conquest of Serdica in 809, the Bulgarian state had already established a direct territorial connection with them.
The "surrounding Sclavinii" were independent in their local affairs, but were subordinated to the Bulgarian ruler in terms of foreign policy and military matters of the principalities of the Sclavenian tribes. They were located around the "Inner Region", which was directly under the rule of the Khan and the Proto-Bulgarians. The Sclavinia constituted the external parts of the Bulgarian state union. They were inhabited by the tribes of the north, the seven tribes that settled in the lowlands between the Danube and the Carpathians and in the region of the Timok. The Timochanis were one of the tribes of the Slavs, whose fate was linked with Danubian Bulgaria from the earliest days of its creation and formation.
The Sclavinia, as administrative territorial units directly connected with the Bulgarian state, survived perhaps until the reign of the throne of Omurtag. The new Bulgarian ruler carried out an administrative and territorial reform, which aimed to centralise power by reducing the influence of individual representatives of the ruling aristocratic elite, both among the Bulgarian boyars and among the Slavic princes. By creating the system of “komitas”, he effectively abolished the independence of the Slavic Sclaveni. Although large parts of the Bulgarian state remained inhabited by those very Slavs, nowhere is there any mention of a real part of the state and the surrounding Sclavinia. The state of Bulgaria began to be perceived as an indivisible whole, not only by the chroniclers, but also by the population of the surrounding countries.
The Slavic Sclavini, although they blended in and became part of the Bulgarian state, are a very important element that played a lasting role in its formation. The state unions and tribal alliances created about two centuries earlier by the Slavs became the solid foundation on which Khan Asparukh set foot and built his new state. Although, according to the chroniclers, his contacts and treaties were connected only with the northerners and the seven Slavic tribes, there is no doubt that their population was the predominant part of the inhabitants of Sclavinia, enclosing the original Danubian Bulgaria. Thus, receiving as allies and helpers a large population, the Bulgarian ruler was able to quickly expand the borders of his country, and use all the resources under his control to strengthen, protect and lead it on the path to prosperity in a short time.
The very behaviour of the Slavs, from the records of medieval chroniclers shows that for the Slavs themselves, this union was truly beneficial. However, another long period had to pass before their princes finally agreed to abandon their independence and invest their efforts and energy to build a strong and successful Bulgaria.