Albert Barnes Commentary Isaiah 21:15

"For they fled away from the swords, from the drawn sword, and from the bent bow, and from the grievousness of war." — Isaiah 21:15 (ASV)

For they fled – The inhabitants of one part of the land.

The grievousness of war – Hebrew, כבד kobed – “the weight, the heaviness, the oppression” of war; probably from the calamities that would result from the march of the Assyrian through their land, either on his way to Judea or to Egypt.