The three horns mean three Kings/Presidents all the horns stand for government rulers, Daniel 7:24. When it comes down to the last three rulers under the final superpower nation what does the Bible say will happen to these three kings?
Revelation 17:9-11
Living Bible
9 “And now think hard: his seven heads represent a certain city built on seven hills where this woman has her residence. 10 They also represent seven kings. Five have already fallen, the sixth now reigns, and the seventh is yet to come, but his reign will be brief. 11 The scarlet animal that died is the eighth king, having reigned before as one of the seven; after his second reign, he too, will go to his doom.