Very interesting. I was under the understanding that Ch. 19 was basically about the uncoming war at Armageddon
Rev 16:14 For they are the spirits of devils, working miracles, which go forth unto the kings of the earth and of the whole world, to gather them to the battle of that great day of God Almighty....
...Rev 16:16 And he gathered them together into a place called in the Hebrew tongue Armageddon.
Rev 19:19 And I saw the beast, and the kings of the earth, and their armies, gathered together to make war against him that sat on the horse, and against his army.
I believe Ch. 20 is mostly about the Millennium:
Rev 20:1 And I saw an angel come down from heaven, having the key of the bottomless pit and a great chain in his hand.
Rev 20:2 And he laid hold on the dragon, that old serpent, which is the Devil, and Satan, and bound him a thousand years,...
Rev 20:7 And when the thousand years are expired, Satan shall be loosed out of his prison,
Rev 20:8 And shall go out to deceive the nations which are in the four quarters of the earth, Gog and Magog, to gather them together to battle: the number of whom is as the sand of the sea.
Rev 20:9 And they went up on the breadth of the earth, and compassed the camp of the saints about, and the beloved city: and fire came down from God out of heaven, and devoured them.
In this second so-called Battle, there IS no real battle at all.
"...and compassed the camp of the saints about, and the beloved city: and fire came down from God out of heaven, and devoured them."
POOF!... just like that! :-D