The Babylonians were a bit too zealous in their role as the captors of Israel.  In particular, they destroyed the temple of God (Jeremiah 50.28).  So, God sends the Medes: “The LORD has stirred up the spirit of the kings of the Medes, because his purpose concerning Babylon is to destroy it, for that is the vengeance of the LORD, the vengeance for his temple” (51.11).

Formerly, Babylon was God’s “hammer and weapon of war: with you I break nations in pieces; with you I destroy kingdoms” (51.20).  Now the Medes will do the same to Babylon, and the demolition will be colossal.  In Jeremiah 50.21-23 we see a long string of items devoted to destruction:

With you I break in pieces the horse and his rider;

                With you I break in pieces the chariot and the charioteer;

With you I break in pieces man and woman;

                With you I break in pieces the old man and the youth;

With you I break in pieces the young man and the young woman;

                With you I break in pieces the shepherd and his flock;

With you I break in pieces the farmer and his team;

                With you I break in pieces the governors and commanders.