Albert Barnes Commentary Psalms 18:47

"Even the God that executeth vengeance for me, And subdueth peoples under me." — Psalms 18:47 (ASV)

It is God who avenges me - Margin, gives avengements for me. The marginal reading is a literal translation of the Hebrew. The meaning is that God had punished the enemies of the author of the psalm for all the wrongs they had done to him. Compare to Romans 12:19.

And subdues the people under me - Margin, destroys. The idea is that he had subdued the nations so that they became obedient to him. The primary notion of the word used here—from דבר dâbar—is to set in a row; to range in order; to connect; to lead; to guide;—then, to reduce to order; to subdue.

This God had done in respect to the nations. Instead of being rebellious and tumultuous, God had reduced them to obedience, and had thus set him over a kingdom where all were subject to order and to law.