The kingdom of God is more than the body of Christ (the Church); it is the entire creation which will be renewed at His 2nd coming.
A king is one who has total authority over everything in his kingdom.
Consider Mat 28:19 (RSV) And Jesus came and said to them, "All authority in heaven and on earth has been given to me."
Jesus is king in heaven and earth.
Rom 8:18-21 (RSV) I consider that the sufferings of this present time are not worth comparing with the glory that is to be revealed to us. For the creation waits with eager longing for the revealing of the sons of God; for the creation was subjected to futility, not of its own will but by the will of him who subjected it in hope; because the creation itself will be set free from its bondage to decay and obtain the glorious liberty of the children of God.
2Pe 3:10-13 (RSV) But the day of the Lord will come like a thief, and then the heavens will pass away with a loud noise, and the elements will be dissolved with fire, and the earth and the works that are upon it will be burned up. Since all these things are thus to be dissolved, what sort of persons ought you to be in lives of holiness and godliness, waiting for and hastening the coming of the day of God, because of which the heavens will be kindled and dissolved, and the elements will melt with fire! But according to his promise we wait for new heavens and a new earth in which righteousness dwells.
Rev 11:15 (RSV) Then the seventh angel blew his trumpet, and there were loud voices in heaven, saying, "The kingdom of the world has become the kingdom of our Lord and of his Christ, and he shall reign for ever and ever."