Isaiah 13:4 & 5
"Listen, a noise on the mountains, like that of a great multitude! Listen, an uproar among the kingdoms, like nations massing together! The Lord Almighty is mustering an army for war. They come from faraway lands, from the ends of the heavens - the Lord and the weapons of his wrath - to destroy the whole country." NIV translation
The prophet assures God's people that He is assembling a coalition of nations (speaking of the Media-Persian empire) to bring down Babylon. This prophecy has both happened and yet is to happen again. The Babylon of Isaiah's day was defeated by the Medes and the Persians. The new Babylon will be dealt with in the future as described by John in Revelation 17.