And the SEVENTH angel sounded;
and there arose loud voices in heaven, saying,
"The KINGDOM OF THE WORLD has become THE KINGDOM OF OUR LORD, and of HIS CHRIST;
Kingdom(s) are what Satan offered Jesus at temptation time (Luke 4:1-13). Satan even admitted 'they were handed over to him' so he got them from somoone else. Now that SOMEONE has acquired the 'Kingdom of the World' again. The world has to be reacquired from the devil such that he will not have any authority there when he is kicked out of heaven (Revelation 12:9).
and He will reign FOREVER AND EVER."
There will not be a possibility that another "fallen angel" will acquire the Kingdom of the World. This is a FINAL solution; the end of Satan's rule. The interpretation of Daniel to a worldly king's dream (Daniel 2:36-44-45) indicates after this king there would be other kingdoms, and then a FOREVER kingdom. Psalm 2:1-6, Psalm 45:6-9, and Revelation 19:6 talk about this 'FOREVER and EVER' kingdom.