Albert Barnes Commentary Jeremiah 50:23

"How is the hammer of the whole earth cut asunder and broken! how is Babylon become a desolation among the nations!" — Jeremiah 50:23 (ASV)

The hammer - Babylon, by whose instrumentality Yahweh had crushed the nations, is now cut asunder, that is, the head of iron or bronze is cut away from the wooden handle, and broken.