Thank you for an interesting question.....it astounds me that those who purport to be "Christian" have no idea what God's Kingdom is....what it is for....and what it will accomplish in the future. To say that the Kingdom of God is within us, is to misconstrue what the Bible teaches about it. Perhaps we should go back to Daniel to find the answer, seeing as how his prophesies pertain to "the time of the end"...the time that we are living in now.
In Daniel ch 2 we find Babylonian King Nebuchadnezzar troubled by a dream. He awakens in a disturbed state but cannot remember what it was about....but as a superstitious Babylonian, he knows that it was important. When none of his magic-practicing priests or wise men could tell him the dream and what it meant, he flew into a rage and threatened to do away with all the wise men of Babylon unless they could tell him what he wanted to know. The wise men were doomed....including Daniel and his companions.
The story goes, that the dream was from the true God; Daniel's God Yahweh. God reveals the dream and its interpretation to Daniel who in turn tells it to the King.
Starting in verse 26 of Daniel ch 2 we read....
"The king said to Daniel. . . .“Can you really make known to me the dream that I saw, and its interpretation?” 27 Daniel replied to the king: “None of the wise men, conjurers, magic-practicing priests, or astrologers are able to tell the king the secret that he is asking. 28 But there is a God in the heavens who is a Revealer of secrets, and he has made known to King Neb·u·chad·nezʹzar what is to happen in the final part of the days. This is your dream, and these are the visions of your head as you lay on your bed:"...
He then goes on to relate what the King dreamed....
31 "You, O king, were watching, and you saw an immense image. That image, which was huge and extremely bright, was standing in front of you, and its appearance was terrifying. 32 The head of that image was of fine gold, its chest and its arms were of silver, its abdomen and its thighs were of copper, 33 its legs were of iron, and its feet were partly of iron and partly of clay. 34 You looked on until a stone was cut out, not by hands, and it struck the image on its feet of iron and of clay and crushed them. 35 At that time the iron, the clay, the copper, the silver, and the gold were, all together, crushed and became like the chaff from the summer threshing floor, and the wind carried them away so that not a trace of them could be found. But the stone that struck the image became a large mountain, and it filled the whole earth."
Daniel then goes on to tell the King that this image is a representation of all the world powers that would have a connection to God's people in some way, down through history, until the time of the "feet of clay", and the last ruling power of these earthly rulerships before God reintroduced his rulership in the hands of his appointed King Jesus Christ.
Beginning with Babylon, he sees Medo-Persia as the next ruling power followed by Greece, then Rome, then Britain and lastly the alliance of Britain and America. These are the feet of clay.
The stone that strikes the image on its feet, destroys all these kingdoms and replaces them as earth's only rulership. So in answer to your OP, the Kingdom of God is an actual government that "crushes" all failed human rulership out of existence and takes their place. It is NOT something "within" us but a real government that will change the way humans are governed forever.
The prophet Isaiah also prophesied this.....
Isaiah 9:6-7...
"For a child will be born to us, a son will be given to us;
And the government will rest on His shoulders;
And His name will be called Wonderful Counselor, Mighty God,
Eternal Father, Prince of Peace.
7 There will be no end to the increase of His government or of peace,
On the throne of David and over his kingdom,
To establish it and to uphold it with justice and righteousness
From then on and forevermore.
The zeal of the Lord of hosts will accomplish this."
Allowing humans to try every kind of rulership that they can dream up has furnished irrefutable evidence that they lack the wisdom to rule themselves independently of their Creator. We are witnessing the death of the last kind of rulership before the end....democracy is in its death throes with almost all democratic nations facing the ire of their people. The weakness of the clay is undermining the strength of the iron. The will of the people is taking the power away from their governments.
Failed rulerships are all we know, but the Kingdom of God will not fail because it is not rulership by the people, or by the will of Monarchs or despots.....but rule by God, as it was supposed to be at the beginning.
In Luke 17:21, Jesus was stating that he, as the King of God's Kingdom, was right there "in their midst" but they failed to recognize him.
This is the way we see the situation....