“You will break them with a rod of iron.” The word “break” is “shepherd” in the Septuagint. That Jesus will conquer the earth and rule with a rod of iron is a well-established prophecy and occurs four times in Scripture (Ps. 2:9; Rev. 2:27; 12:5; 19:15).
[For more detail on Jesus ruling with a rod of iron, see commentary on Revelation 2:27.]