Jer 50:20 In those days, and in that time, saith the LORD, the iniquity of Israel shall be sought for, and there shall be none; and the sins of Judah, and they shall not be found: for I will pardon them whom I reserve. Again reference to future end-time events.
Jer 50:21 Go up against the land of Merathaim, even against it, and against the inhabitants of Pekod: waste and utterly destroy after them, saith the LORD, and do according to all that I have commanded thee.
According to the Bible Encyclopedia:
Meaning: double rebellion
probably a symbolical name given to Babylon (Jer. 50:21), denoting rebellion exceeding that of other nations
According to Eastons Bible:
Pekod - probably a place in Babylonia (Jer. 50:21; Ezek. 23:23). It is the opinion, however, of some that this word signifies "visitation," "punishment," and allegorically "designates Babylon as the city which was to be destroyed."
"...utterly destory them" is a command which for ancient Babylon took place over an extended period of time. It is therefore conceivable that for future "Babylon" her destruction could occur in a single act or a single series of events that occur simultaneously.
Jer 50:22 A sound of battle is in the land, and of great destruction. While the army/government of ancient Babylon was defeated in battle by Alexander the Great, there was no "great destruction". In fact the armies of Alexander were specifically forbidden to enter the homes of the residents of Babylon. So once again this is a prophecy with a future fulfillment.
Jer 50:23 How is the hammer of the whole earth cut asunder and broken! how is Babylon become a desolation among the nations! What other nation has been a "hammer of the whole earth" imposing her will with "hammer-fisted" force and authority? The mighty United States of America, of course. But this indicates that that "hammer" will eventuallyl be destroyed.