Complex sentence: The Slavs (Serbs) and Avars had their "state union" north of Belgrade with the Serbs and other Slavic tribes finally settling in the region of Belgrade as well as the regions west and south of Belgrade in the beginning of the 7th century.
Split into simpler sentences: The Slavs (Serbs) and Avars had their'state union' north of Belgrade. The Serbs and other Slavic tribes finally settled the region of Belgrade as well as the regions west and south of Belgrade in the beginning of the 7th century.