“Therefore go and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit … ”    (Matthew 28:19)
The concept of the kingdom of God is often divided into two, from the point of view of its form. Most people understand the Kingdom of God from the heavenly aspect, while some of the mundane aspects. People who understand the heavenly aspect of the kingdom of God believes that it is later, not now. But, on the contrary, those who understand it from the mundane aspects, was convinced that the Kingdom of God is manifest in earthly life, such as politics, economy and the various aspects of life.
What exactly is the meaning of the kingdom of God? Kingdom of God is a governance in which God govern with the full divine power as king of the universe, because God is the Creator of the universe. The concept of empire is very thick in the Bible. From the beginning, Genesis, and until the end, the Revelation, the Bible declare the kingdom of God, even there will be a thousand year kingdom on earth where believers reign with Christ Jesus.
Jesus Christ came to reestablish what was missing from Adam. What is it? The Kingdom and royal power. Therefore the Lord Jesus said that “the kingdom of God has come” because he has taken and received all authority in heaven and on earth (Matt. 28:18).
Simply, in the smaller scope, that is personal, the kingdom of God is God’s rule over our lives as His human creation. The Lord Jesus is the King who reigns over our lives. The Bible says that Jesus is the King of kings.
Thus, the Kingdom of God include also temporal aspects (the present) and heavenly (the eternal). Therefore, the kingdom of God  should be  manifested also in all aspects of human life on earth.
Then, can we “extend” the kingdom of God on earth? The answer is yes. How? By carrying out the Great Commission of the Lord Jesus, the King of kings, which is:  “Go and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit, and teaching them to obey everything I have commanded you. And surely, I am with you always, even unto the end of time. ”
What else should we do to ‘expand’ the kingdom of God? Nothing more except to be witnesses of Christ Jesus wherever we are.
Hallelujah, God bless you abundantly!