| Barnes' Notes on the Bible The hammer - Babylon, by whose instrumentality Yahweh had crushed the nations, is now cut asunder, i. e., the head of iron or bronze is cut away from the wooden handle, and broken.
Clarke's Commentary on the BibleThe hammer of the whole earth - Nebuchadnezzar dashed to pieces the nations against whom he warred. He was the scourge of the Lord.
Gill's Exposition of the Entire BibleHow is the hammer of the whole earth cut asunder and broken!.... The Targum is, "how is the king cut down and broken that moved the whole earth!'' The king of Babylon, or the kingdom of Babylon, which was like a hammer for its hardness and strength; and being an instrument, in the hand of God, of beating to pieces and destroying the kingdoms and nations around it; but is now destroyed itself. These are the words either of the prophet, or rather of the people of other nations, wondering how this destruction came about, and rejoicing at it; how is Babylon become a desolation among the nations! this explains who and what is meant by the hammer of the earth, and by its being cut asunder and broken; even the utter destruction of the city and kingdom of Babylon.
Keil and Delitzsch Biblical Commentary on the Old TestamentBabylon, "the hammer of the whole earth," i.e., with which Jahveh has beaten to pieces the nations and kingdoms of the earth (Jeremiah 51:20), is itself now being beaten to pieces and destroyed. On the subject, cf. Isaiah 14:5-6. Babylon will become the astonishment of the nations, Jeremiah 51:41. "How!" is an exclamation of surprise, as in Zephaniah 2:15 -a passage which probably hovered before the mind of the prophet.
Geneva Study BibleHow is the {u} hammer of the whole earth cut asunder and broken! how is Babylon become a desolation among the nations! (u) Nebuchadnezzar, who had smitten down all the princes and people of the world.
Jamieson-Fausset-Brown Bible Commentary23. hammer-that is, Babylon, so called because of its ponderous destructive power; just as "Martel," that is, "a little hammer," was the surname of a king of the Franks (Isa 14:6).
Matthew Henry's Concise Commentary50:21-32 The forces are mustered and empowered to destroy Babylon. Let them do what God demands, and they shall bring to pass what he threatens. The pride of men's hearts sets God against them, and ripens them apace for ruin. Babylon's pride must be her ruin; she has been proud against the Holy One of Israel; who can keep those up whom God will throw down? | 
