John Gill Commentary Jeremiah 51:28

"Prepare against her the nations, the kings of the Medes, the governors thereof, and all the deputies thereof, and all the land of their dominion." — Jeremiah 51:28 (ASV)

Prepare against her the nations, with the kings of the Medes ,
&c.] At the head of them, Darius and Cyrus. The Syriac version has it in the singular number, the king of the Modes: the captains thereof, and all the rulers thereof, and all the land of
his dominions ;
that is, the inhabitants of it, the common people, with their princes, nobles, governors, as captains of them, under Cyrus, their generalissimo.