First of all, I would like to ask you which Bible you are reading?
I have tried to find were, in the Lord's prayer, you found that His Kingdom will be on the earth, but I can't find it!
What I found was in Matthew 6:10 is:
"let thy KINGDOM come; thy Will be done upon Earth, even as in Heaven". (Emphatic Diaglott)
I also tryed The American Standard Version. It says:
"Thy kingdom come. Thy will be done, as in heaven, so on earth."
And then The King James Bible:
"Thy kingdom come. Thy will be done in earth, as it is in heaven."
All I can see is that God's will includes both heaven and earth.
And about the 144 000, they will rule as kings and priest with Jesus in heaven. You can read about them in Revelation 7:4, and in verse 9 you can read:
"After these things I saw, and behold, a great multitude, which no man could number, out of every nation and of all tribes and peoples and toungues, standing BEFORE the throne and BEFORE the Lamb, arrayed in white robes, and palms in ther hands;"
And in Isaiah 66:1 we can read:
Thus saith Jehovah, Heaven is my throne and the earth is my footstool..."
So, if this "great multitude" were standing BEFORE the throne, they must be on the "footstool". Right?
And the footstool was the earth!
Then back o the Lord's prayer.. This must tell us that people will live here on earth in peace and happiness. And a lot of other verses in the Bible tells us the same.