The Seven Slavic tribes were a union of Slavic tribes

Slavic peoples

The Slavic people are an Indo-European panethnicity living in Eastern Europe, Southeast Europe, North Asia and Central Asia. The term Slavic represents a broad ethno-linguistic group of people, who speak languages belonging to the Slavic language family and share, to varying degrees, certain...

 of Moesia

Moesia

Moesia was an ancient region and later Roman province situated in the Balkans, along the south bank of the Danube River. It included territories of modern-day Southern Serbia , Northern Republic of Macedonia, Northern Bulgaria, Romanian Dobrudja, Southern Moldova, and Budjak .-History:In ancient...

 (the Danubian Plain

Danubian Plain (Bulgaria)

The Danubian Plain constitutes the northern part of Bulgaria, situated north of the Balkan Mountains and south of the Danube. Its western border is the Timok River and to the east it borders the Black Sea. The plain has an area of . It is about long and wide.The relief of the Danubian Plain is...

 in modern Bulgaria

Bulgaria

Bulgaria , officially the Republic of Bulgaria , is a parliamentary democracy within a unitary constitutional republic in Southeast Europe. The country borders Romania to the north, Serbia and Macedonia to the west, Greece and Turkey to the south, as well as the Black Sea to the east...

) that was established around the middle of the 7th century and took part in the formation of the First Bulgarian Empire

First Bulgarian Empire

The First Bulgarian Empire was a medieval Bulgarian state founded in the north-eastern Balkans in c. 680 by the Bulgars, uniting with seven South Slavic tribes...

 together with the Bulgars

Bulgars

The Bulgars were a semi-nomadic who flourished in the Pontic Steppe and the Volga basin in the 7th century.The Bulgars emerge after the collapse of the Hunnic Empire in the 5th century....

 in 680-681.

In the late 7th century the Seven Slavic tribes moved west and were assigned the defence of the newly-established Bulgarian Empire's western and northwestern border (the Iskar River up to its mouth in the Danube

Danube

The Danube is a river in the Central Europe and the Europe's second longest river after the Volga. It is classified as an international waterway....

) against Avar

Eurasian Avars

The Eurasian Avars or Ancient Avars were a highly organized nomadic confederacy of mixed origins. They were ruled by a khagan, who was surrounded by a tight-knit entourage of nomad warriors, an organization characteristic of Turko-Mongol groups...

 raids, as well as some of the passes of the Balkan Mountains

Balkan Mountains

The Balkan mountain range is a mountain range in the eastern part of the Balkan Peninsula. The Balkan range runs 560 km from the Vrashka Chuka Peak on the border between Bulgaria and eastern Serbia eastward through central Bulgaria to Cape Emine on the Black Sea...

, whereas the Severi, whose possible participation in the union is not clear, would guard the eastern part of the mountains.

The Seven Slavic tribes, together with other Slavic tribes of the Bulgarian Empire, gradually formed the Bulgarian ethnicity

Bulgarians

The Bulgarians are a South Slavic nation and ethnic group native to Bulgaria and neighbouring regions. Emigration has resulted in immigrant communities in a number of other countries.-History and ethnogenesis:...

 in the 9th century due to the Christianization of Bulgaria

Christianization of Bulgaria

The Christianization of Bulgaria was the process by which 9th-century medieval Bulgaria converted to Christianity. It was influenced by the khan's shifting political alliances with the kingdom of the East Franks and the Byzantine Empire, as well as his reception by the Pope of the Roman Catholic...

 under Boris I

Boris I of Bulgaria

Boris I, also known as Boris-Mihail and Bogoris was the Knyaz of First Bulgarian Empire in 852–889. At the time of his baptism in 864, Boris was named Michael after his godfather, Emperor Michael III...

and the preceding administrative reforms that deprived them of their autonomy and self-government.