Looking to John Dominic Crossan for a moment, he writes in his book God and Empire this of the Kingdom of God:
The concern here, according to Crossan, is with changing the way the world runs and works. It puts God's kingdom in opposition to Caesar's. So, what does that mean for us? We don't live in Caesar's kingdom. In fact, at least in theory, it's "we the people" who govern ourselves. It is our kingdom -- so how does that relate to God's kingdom? In what ways are we participating in the transformation of the world in which we live. Calvin would have us live in opposition to the world. Is that what is expected of us? Constantine would have the world define the Kingdom? What is that Jesus wants of us?
"The Kingdom of God" was a standard expression for what I have been calling the Great Divine Cleanup of this world. It was what this world would look like if and when God sat on Caesar's throne, or if and when God lived in Antipas' palace. That is very clear in these parallel phrases of the Lord's Prayer in Matthew 6:10: "Your kingdom come. Your will be done, on earth as it is in heaven." The Kingdom of God is about the Will of God for this earth here below. That earthly presence agrees, of course, with everything we have seen so far about apocalyptic eschatalogical expectation. It is about the transformation of this world into holiness, not the evacuation of this world into heaven. (God and Empire, HarperOne, pp. 116-117).