History of Eastern Europe

https://en.wikipedia.org/wiki/Bulgars

https://www.britannica.com/topic/Bulgar

https://www.csc.kth.se/~dilian/bulgars.pdf

http://blacksea.ehw.gr/Forms/fLemmaBody.aspx?lemmaid=10659

https://www.thoughtco.com/bulgars-bulgaria-and-bulgarians-1788807

https://en.wikipedia.org/wiki/Pannonian_Avars

https://www.ancient.eu/Avars/

https://www.britannica.com/topic/Avar