Actually, God has always reigned om earth, even though evil things happen. When Jesus returns, all nations will be gathered before him and he will separate the saved from the unsaved.That's the end of one age and the start of a new age, the thousand years and the gospel will be shared during it as it is being shared in your false version of it with satan deceiving people, sin and rebellion and murders of Christians. Those evil things don't exist in the real thousand years.
this gospel of the kingdom shall be preached in all the world for a witness unto all nations; and then shall the end come. Mt.24:14
The end.