This is the 3877th most frequent Russian word.
белорусского
"Belarusian" (adjective, relating to Belarus).
The word 'белорусского' acts as an adjective describing 'города,' indicating the city is from Belarus.
Мой друг родом из белорусского города Минск.
My friend is from the Belarusian city of Minsk.
Here 'белорусского' serves as an adjective modifying 'писателя,' specifying that the writer is from Belarus.
Вы читали произведения белорусского писателя Петруся Бровки?
Have you read works by the Belarusian writer Petrus Brovka?
In this sentence, 'белорусского' modifies 'народа' as an adjective, denoting that the history pertains to people from Belarus.