Albert Barnes Commentary Jeremiah 10:7

"Who should not fear thee, O King of the nations? for to thee doth it appertain; forasmuch as among all the wise men of the nations, and in all their royal estate, there is none like unto thee." — Jeremiah 10:7 (ASV)

O King of nations – that is, pagan nations. Yahweh is not the national God of the Jews only, but He reigns over all mankind (Psalms 22:28).

It – that is, everything.

In all their kingdoms – More correctly, “in all their royalty or kingship.”