The Man Christ Jesus, the Son of God, reigns in the kingdom of God from heaven now.

And, you can become a citizen of this Kingdom! (See page 3 and 4)

God has recorded in His word...

About the kingdoms of men on earth
He (God) removes kings, and sets up kings. (1) ...the most High rules in the kingdom of men, and gives it to whomsoever He will, and sets up over it the basest of men. (3). ...the most High rule(s) in the kingdom of men, and gives it to whomsoever He will (4) ...the heavens do rule. (4) - Daniel, Prime Minister of the Babylonian Empire. (6th Century BC)
His (God's) dominion is an everlasting dominion, and His kingdom is from generation to generation: (5) God of Daniel: ...is the living God, and steadfast for ever, and His kingdom ...shall not be destroyed, and His dominion shall be even unto the end. (6) - King Nebuchadnezzar, Emperor of Babylon. (6th Century Before Christ on Earth as Man - BCE)

And about the Kingdom of God on earth
And in the days of these kings (Roman conglomerate) shall the God of heaven set up a kingdom, which shall never be destroyed: and the kingdom shall not be left to other people, but it shall break in pieces and consume all these kingdoms, and it shall stand for ever. (2)
...the Son of man came with the clouds of heaven, and came to the Ancient of days (God the Father), and they brought Him (Jesus) near before Him (God the Father). And there was given Him (Jesus) dominion, and glory, and a kingdom, that all people, nations, and languages, should serve Him: His dominion is an everlasting dominion, which shall not pass away, and His kingdom that which shall not be destroyed. (7)
...the saints of the most High shall take the kingdom, and possess the kingdom for ever, even for ever and ever. (8) And the kingdom and dominion, and the greatness of the kingdom under the whole heaven, shall be given to the people of the saints of the most High, whose kingdom is an everlasting kingdom, and all dominions shall serve and obey him. (9)

There have been two spiritual kingdoms on this earth - the Kingdom of God / Heaven also known as the Kingdom of His dear Son. The other is Satan's kingdom of darkness under whom are his followers - deceived angels and most mankind.

“The kingdom of God comes not with observation: Neither shall they say, Lo here! or, lo there! for, behold, the kingdom of God is within you”. –Luke 17:20, 21.

When asked about His kingdom and His Sovereignty, the Lord said to Pilate, the Roman Governor, in unequivocal terms, “My kingdom is not of this world; if My kingdom were of this world, then would My servants fight, that I should not be delivered to the Jews: but now is My kingdom not from hence”. –John 18:36. Jesus reigns from heaven, not from hence (earth).

And about the establishment of the Kingdom of God on earth
Scriptures tell us that God sent His holy Spirit from heaven on the day of Pentecost, fifty days after the resurrection of the Lord. The Church of Jesus Christ was born on that day. It is about this event that Jesus said to His disciples, "Verily I say unto you, that there be some of them that stand here, which shall not taste of death, till they have seen the kingdom of God come with power" -Mark 9:1.

The LORD said unto my Lord, Sit thou at my right hand, until I make thine enemies thy footstool. - Psalms 110:1. The LORD God fulfilled this prophecy by exalting the Lord Jesus, "according to the working of His mighty power, which He wrought in Christ, when He raised Him from the dead, and set Him at His own right hand in the heavenly places, far above all principality, and power, and might, and dominion, and every name that is named, not only in this world, but also in that which is to come: and hath put all things under His feet", -Ephesians 1:19-22.

And about the Kingdom of God on earth now
The Lord establishes His spiritual kingdom of heaven in the hearts of men and women whose sins have been forgiven. Scriptures say, "He has delivered us from the power of darkness, and has translated us into the kingdom of His dear Son". –Colossians 1:13. He becomes their King. He reigns in their lives through the holy Spirit of God.

God has raised together with Christ all His believers who were dead in their trespasses and sins. (Ephesians 2:1) He has restored life in them by His grace. Moreover, God has also made His people sit together with Christ to reign with Him. (Ephesians 2:6). They have been made kings. While government is upon the shoulders of the King Himself, Jesus exhibits His power over all - principality, power, might and dominion through His faithful ones now. They enforce His rule here on earth and exercise His authority till He returns.

And about the Kingdom of God hereafter
Jesus conquered death for His believers. These Chosen ones will conquer death at His coming when "God ... shall bruise Satan under their feet" as per Rom 16:20. It will be a rapturous event for the saints. "Behold, I shew you a mystery; We shall not all sleep, but we shall all be changed, in a moment, in the twinkling of an eye, at the last trump: for the trumpet shall sound, and the dead shall be raised incorruptible, and we shall be changed. For this corruptible must put on incorruption, and this mortal must put on immortality. So when this corruptible shall have put on incorruption, and this mortal shall have put on immortality, then shall be brought to pass the saying that is written, Death is swallowed up in victory. O death, where is thy sting? O grave, where is thy victory?" -1 Corinthians 15:51-55.

Then comes the end, when He shall have delivered up the kingdom to God, even the Father; when He shall have put down all rule and all authority and power. For He must reign, till He hath put all enemies under His feet. The last enemy that shall be destroyed is death. For He hath put all things under His feet. But when He saith, all things are put under Him, it is manifest that He is excepted, which did put all things under Him. And when all things shall be subdued unto Him, then shall the Son also Himself be subject unto Him that put all things under Him, that God may be all in all. -1 Corinthians 15:25-28.

And about how one can become a citizen of this Kingdom of God
It is simple but a serious matter of faith, faith in the word of God.

God’s word says: “All have sinned and come short of the glory of God. There is none righteous, no, not one” (Rom 3:23). While it is obvious and is true of every one of us, we have always refused to accept this fact but have tried to justify our sinful acts by blaming people and situations around us. We have also tried to compensate our wrong doings (this is what the Bible calls as sin) with self-righteous philanthropic acts – giving alms and sacrificing our money and wealth for the needy.

However, God, the just Judge of all mankind has ruled: The wages of sin is death (Romans 6:23). And, the soul that sins shall die. (Ezekiel 18:20). This death goes beyond just the death of the body; it is an eternal separation from the Holy God, the whole being – spirit, soul and body - sentenced to a place of unending torment as punishment for the sins committed. Self-inflicted indeed! (Originally hell was created as an eternal destiny for the devil and the angels who rebelled with him against their Creator, refusing to serve Him to become a god themselves, unyielding to His sovereignty).

But God is a God of love; He wants none of us to go to this Godless destiny. He came down in His Son Jesus Christ to give us eternal life as a gift. This historical Jesus bore the punishment of our sins on the cross two thousand years ago to save us from the devil, destruction and death. Irrespective of race, cast, creed, nationality or language, this Saviour of the world accepts everyone who comes repenting to Him to receive the forgiveness He offers.

God comes to live within every believer in His Holy Spirit by making us His temple. He establishes His Kingdom in the hearts of all who submit to Him as their Lord. All such citizens, as a Church of God, keep spreading this gospel, all the while anticipating their King’s return, to be with Him for ever.

Though the present is tense, a perfect future awaits the believers in Christ!