Before, when I have thought about the millennial reign of Jesus, I never thought about the fall of Babylon; but I guess that that is required. What else would happen with the wicked parts of the world? They must fall, if all is going to be peaceful. The wicked will fight against Zion. Zion will have to defend themselves, and Babylon will fall. This scene is described in 2 Nephi 23, and in Isaiah 13.