Chapter 12 begins with a vision of events that have already taken place, similarly to the manner and in succession to the events of chapter 11. It also sets the time frame for the events that succeed it. This chapter (12) is the beginning of the last major division of the prophetic passages (which runs through chapter 22:5).
The first minor division of the book of Revelation includes chapters 1 through 3 and gave us the introductions, salutations, and vision of the letters to the churches.
The second minor division included the visions beginning with the throne room in chapters 4 and 5, and the introduction to the disclosure of the mystery of God.
This is followed with the major division in chapter 6 through 11; and in the unfolding of the mystery and the prophesy of the end of the Jewish state, which is introduced through the breaking of the seven seals identifying the purpose of God unfolding in all its attendant detail.
The second major vision includes chapters 12 through 22:6, with the recounting of the plan of God in the destruction of the two beasts.
The last minor division begins with chapter 22 verse 6 and continues through to the end of the book with the closing admonitions.
There remains some expansion of the themes presented in the first major division, plus the introduction of parallel themes and events that lead to the fulfilling of the judgments against Rome.
From chapter 12 to 14, the progress of the book is suspended as it was in chapter 11. Here we are introduced to the spiritual battle that had already taken place between Satan and Christ. The sign of war in heaven is described, as well as events upon the earth.