Albert Barnes Commentary Jeremiah 50:3

"For out of the north there cometh up a nation against her, which shall make her land desolate, and none shall dwell therein: they are fled, they are gone, both man and beast." — Jeremiah 50:3 (ASV)

Out of the north - Media lay to the northwest of Babylon. This constant use of the north, the quarter where the sun never shines, and therefore the region of darkness, is symbolic of the region from where danger ever comes.

They shall remove ... - Translate it : from man even to cattle they are fled, they are gone.