kingdom is a place under the authority of a king; a place of life & activity. A kingdom without inhabitants would be no kingdom at all. And, a kingdom in which the king did nothing & required nothing of his subjects would again (in function & reality) not be a kingdom at all. The religious leaders of Christ's day accused Him of participating in the devil's kingdom. Of course, nothing could have been further from the truth. However, those same religious leaders were the recipients of some rather cutting criticisms from Christ along these same lines. Consider His words as recorded in Luke 11:44, "Woe unto you, scribes & Pharisees, hypocrites! for you are as graves which appear not, & the men that walk over them are not aware of them." That's about as dead & forgotten as is possible. But Jesus was & is king over a living kingdom (Luke 20:38).
Our King is great and He deserves great praise. He is greater than Jonah or Solomon were (Luke 11:31 & 32). His kingdom is an everlasting and (presently) an invisible kingdom. Above all else, it is the hearts of humans that God desires to possess (John 18:36). He desires truth in the inward parts (Psalm 51:6). He is looking to produce spiritual discernment and the love of the Father in us (Luke 11:42). The good deeds that should be done by those of us who are children of the kingdom should always flow forth from a life that is instructed by the Spirit and in tune with the Word. The key to the kingdom of God is certainly only available to the humble (Luke 11:52). Through Christ, the kingdom of heaven is at hand; it has come upon all of us.