The battle of Armageddon is a great, future war that will be fought at Mount Megiddo. This will be the most terrifying and destructive of all wars mankind will experience. The main difference between this and other wars is that the outcome is sure: we know who the winner is! This battle will be fought by men and by spiritual forces. Jesus Christ will return in the midst of this war to prove His power and might. He wins! He will judge the nations of the world and establish His kingdom.
See Revelation, chapter 16, where the preparation for the battle is described in verses 12-16. Read also, chapters 17-20. This “battle” is the final world war and it is more than just a physical war. All of the forces of good and evil will be fighting for power. Jesus wins, and then establishes His reign on earth for one thousand years.