stylistic:style_transfer
Middle (670–720) and late (720–822) Avar periods

With the death of Samo in 658 and Kubrat in 665, some Slavic tribes again came under Avar rule. Despite their father's advice, Kubrat's sons failed to maintain cohesion in Old Great Bulgaria which began to disintegrate. A few years later in the time of Batbayan, Old Great Bulgaria dissolved into five branches. From western Onoguria the first group of folk moved to Ravenna under Alzeco in the 650s. According to Book II of the Miracles of Saint Demetrius, a certain Avar Chagan seized his opportunity to coalesce in the regions further north in response to the secession of the Diocese of Sirmium in the 670s by a " Kuber " Chagan.

About this time, Mark of Kalt records that in 677, the principality of Ungvar (Ung fortress) was established in the regions further north where Kotrag 's group also fled following the chaos, and a third group of Onogur-Bulgarians led by Batayan was subdued by Ziebel 's emerging Khazar Empire according to Nikephoros I of Constantinople. Under Mauros, a fourth group of folk eventually settled in the present-day region of North Macedonia. The fifth group from Onogur, Bulgaria, led by Khan Asparukh —the father of Khan Tervel —settled permanently along the Danube (c. 679–681), establishing the First Bulgarian Empire, stabilized by the victory at the battle of Ongal south of the eastern Carpathians. The Bulgarians turned on Byzantium who had established an alliance with Ziebel's Khazars.

Although the Avar empire had diminished to half its original size, the Avar-Slav alliance consolidated their rule west from the central parts of the mid-Danubian basin and extended their sphere of influence west to the Vienna Basin. The new ethnic element marked by hair clips for pigtails; curved, single-edged sabres; and broad, symmetrical bows marks the middle Avar-Bulgar period (670–720). New regional centers, such as those near Ozora and Igar appeared. This strengthened the Avars' power base, although most of the Balkans lay in the hands of Slavic tribes since neither the Avars nor Byzantines were able to reassert control.

There are very few sources that cover the last century of Avar history. They only talk about the relations between the Avars and Lombards but little about the internals of the khaganate, so information about the Carpathian Basin is mostly from archaeology. Even here, elites are almost invisible, and there is little evidence of nomadic behavior. This transformation is little understood, but may have something to do with population growth.

A new type of ceramics—the so-called " Devínska Nová Ves " pottery—emerged at the end of the 7th century in the region between the Middle Danube and the Carpathians. These vessels were similar to the hand-made pottery of the previous period, but wheel-made items were also found in Devínska Nová Ves sites. Large inhumation cemeteries found at Holiare, Nové Zámky and other places in Slovakia, Hungary and Serbia from the period beginning around 690 show that the settlement network of the Carpathian Basin became more stable in the Late Avar period. The most popular Late Avar motifs— griffins and tendrils decorating belts, mounts and a number of other artifacts connected to warriors—may either represent nostalgia for the lost nomadic past or evidence a new wave of nomads arriving from the Pontic steppes at the end of the 7th century. According to historians who accept the latter theory, the immigrants may have been either Onogurs or Alans. Anthropological studies of the skeletons point at the presence of a population with mongoloid features.

The Khaganate in the Middle and Late periods was a product of cultural symbiosis between Slavic and original Avar elements with a Slavic language as a lingua franca or the most common language. In the 7th century, the Avar Khaganate opened a door for Slavic demographic and linguistic expansion to Adriatic and Aegean regions (see Slavic migrations to Southeastern Europe).

In the early 8th century, a new archaeological culture —the so-called "griffin and tendril" culture—appeared in the Carpathian Basin. Some theories, including the "double conquest" theory of archaeologist Gyula László, attribute it to the arrival of new settlers, such as early Magyars, but this is still under debate. Hungarian archaeologists Laszló Makkai and András Mócsy attribute this culture to an internal evolution of Avars resulting from the integration of the Bulgar émigrés from the previous generation of the 670s. According to Makkai and Mócsy, "the material culture—art, clothing, equipment, weapons—of the late Avar/Bulgar period evolved autonomously from these new foundations". Many regions that had once been important centers of the Avar Empire had lost their significance while new ones arose. Although Avaric material culture found over much of the northern Balkans may indicate an existing Avar presence, it probably represents the presence of independent Slavs who had adopted Avaric customs. Radovan Bunardžić dated Avar-Bulgar graves excavated in Čelarevo (near Sirmium), containing skulls with Mongolian features and Judaic symbols, to the late 8th century and 9th century.