Jeremiah 51:11

This oracle names the "Medes" as God’s instrument to destroy Babylon, as punishment for their destroying His temple. The fall of Babylon to the Medes was a fulfillment of this prophecy, but it did not fulfill all the prophecies about the fall of Babylon in these chapters. The Medes lived north of Babylon (in modern northwest Iran, Iranian Kurdistan). The Medes had been allies of the Babylonians in the destruction of Nineveh, the capital of the Assyrian Empire, in 612 B.C. Seventy-three years later, they joined with the Persians to defeat Babylon, in 539 B.C. (cf. Daniel 5:28; Daniel 5:31; Daniel 8:20).

"In 550 B.C. Cyrus the Persian ruler invaded the region [Babylon] and subjugated it. . . . There is some evidence that about 561-560 B.C. an invasion of Babylon by the Medes was expected. We have no historical evidence of any outcome. [Note: See Wiseman, p. 38.] On the other hand the term Medes may be a general one. It is known that the mother of Cyrus the Persian was a Mede, and the Medes and Persians were linked together several times in the book of Daniel (e.g., Daniel 5:28; Daniel 6:8; Daniel 6:12; Daniel 6:15). In that case the reference here may be to Cyrus, but the matter is still open to debate (cf. Isaiah 13:17)." [Note: Thompson, pp. 752-53.]