We finally return to the history of Babylon. In order to understand this reference to “the Medes”, we need to review some of the history. In Isaiah’s day, the Babylonians were ruled by the powerful Assyrian empire. This continued until about 607 BC when Nebuchadnezzar and his father regained control of Babylon. The kingdom of Babylon continued the splendor and greatness of the preceding empire for several decades. Josephus records, "[Nebuchadnezzar] built walls about the inner city…and adorned its gates gloriously, he built another palace…to describe the vast height and immense riches of which, it would perhaps be too much for me to attempt. (Josephus, Antiquities of the Jews, Book X, Chap. XI, v. 1)
“Babylon was one of the great cities of the ancient world, perhaps the greatest. Its walls were, for height and width, one of the wonders of the world. The temple of Bel, the terraced (”hanging“) gardens, the immense copper gates, and the artificial lake were, up to that time, the greatest achievements of human skill and ingenuity. The fields and farms and flocks yielded almost incredible returns, and the wealth, luxury and power of the ruling classes were correspondingly great. If any city, or country, could be regarded as invincible, Babylonia and Babylon might be so considered. But centuries before their fall Isaiah predicted, with supernatural knowledge of the details, the destruction of the city and the overthrow of the government.” (Reynolds and Sjodahl, Commentary on the Book of Mormon, vol. 1, p. 364)
The glory of Babylon would not last. Its decline began with the pride of Belshazzar. He was a king of Babylon in about 539 BC when the Jews were still captive in Babylon. One evening, Belshazzar had taken the holy vessels, which had previously been pillaged from the temple of Solomon, and used them for one of his feasts. The anger of the Lord was manifest when he saw a hand writing a message of doom on the wall of his palace. Daniel interpreted the message. Part of the message was interpreted as follows, ’Thy kingdom is divided, and given to the Medes and Persians…In that night was Belshazzar the king of the Chaldeans slain. And Darius the Median took the kingdom, being about threescore and two years old’ (Dan 5:28-31).
“Babylon…became so wicked that her power over surrounding nations lasted only until 539 B.C. That was the year the Medes and Persians came sweeping down from the mountains and high plateaus to the east and conquered Babylon in a single night. They were led by Cyrus, whom Isaiah identified by name around 175 years before Cyrus was born (see isa. 44:28; 45:1). After Babylon was overthrown, Cyrus allowed the Jews to return to Jerusalem in 538 B.C.” (W. Cleon Skousen, Isaiah Speaks To Modern Times, 260 as taken from Commentaries on Isaiah in the Book of Mormon, ed. by K. Douglas Bassett, [American Fork, UT: Covenant Publishing Co., 2003], 198)