Albert Barnes Commentary Psalms 18:45

"The foreigners shall fade away, And shall come trembling out of their close places." — Psalms 18:45 (ASV)

The strangers shall fade away - Hebrew, “The sons of the stranger.” That is, foreigners. The word translated “fade away”—נבל nâbêl—properly means to wilt, wither, or fall away, as is applicable to flowers, leaves, or plants: Psalms 1:3; Psalms 37:2; Isaiah 1:30; Isaiah 28:1. Here it means that those foreign nations would diminish in numbers and in power, until they would completely disappear. The idea is that all his foes would vanish, and that he and his kingdom would be left in peace.

And be afraid out of their close places - The word translated “be afraid” means to tremble—as those who are in fear do. The word translated “close places” means places that are shut up or enclosed, such as fortified cities or fortresses. The reference is to their places of retreat: towns, castles, and fortresses. The meaning is that they would find such places to be no security and would tremble out of them; that is, they would flee out of them in consternation and alarm. The general thought is that of ultimate, complete security for himself and his kingdom, or entire deliverance from all his enemies.