John Gill Commentary Jeremiah 49:5

"Behold, I will bring a fear upon thee, saith the Lord, Jehovah of hosts, from all that are round about thee; and ye shall be driven out every man right forth, and there shall be none to gather together the fugitives." — Jeremiah 49:5 (ASV)

Behold, I will bring a fear upon thee, saith the Lord God of
hosts
The terrible army of the Chaldeans, which would strike them with a panic; who thought they were so secure in their fortresses, trusting in their riches:

from all those that be about thee ;
meaning either from the Chaldeans, and the neighbouring nations, that would join and surround the Ammonites on all sides; or from all the borders of Ammon round about, from where they would come; they would be a "magormissabib", "a fear all round", (Jeremiah 20:3) :

and ye shall be driven out every man right forth ;
driven out of their houses, and cities, and villages, and steer their course right forward, and never look behind to see what had become of their families and their friends; everyone having enough to do to provide for his own safety:

and none shall gather up him that wandereth ;
that is straggling about, and does not know which way to take, and where to flee for safety; all will be so intent on their own safety, that they will not concern themselves for others, to take them under their care; to take those who are on foot onto their horses or carriages when they overtake them, or into their houses as they pass by.