Bulgaria

wiktionary

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Bulgar +‎  -ia, from the  Middle Latin, in English used from the 16th century. 

etymonline

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Bulgaria (n.)

Medieval Latin, from Bulgari "Bulgarians," traditionally explained as "the men from the Bolg," the River Volga, upon whose banks they lived until 6c. But evidence is wanting, and the people's name for themselves in Old Bulgarian was Blugarinu, according to OED and Century Dictionary, which suggests a different origin. In other sources [such as Room], the name is said to be ultimately from Turkic bulga "mixed," in reference to the nature of this people of Turko-Finnish extraction but Slavic language.