Compare "The kingdoms of this world are become the kingdoms of our Lord" to Revelation 10:7 which says, "the mystery of God should be finished...". Both places are referring to the seventh angel sounding. Also, the verb "are become" is immediate past tense, meaning that it happened just now. Furthermore, this verse is indicating that this is the moment that the millennial reign of Christ begins. It's only chapter 11 so the rest of Revelation is a retelling of the story.