The Believers we see sitting on Thrones are the Four and Twenty Elders of chapter 4:4-5.

         They stand for the Church and were resurrected or caught up out before The Tribulation and are the harvest that Christ and those who rose at the time of His Resurrection were the First Fruits.

The First Resurrection is in 1 Thessalonians 4:16, that the dead in Christ shall rise first. 

          But as no wicked are mentioned it is simply a statement that the living Christians shall not be caught away before the Dead in Christ is raised.

                   This speaks of two set of Believers who are to be raised at the First Resurrection. 

The First Resurrection.
Revelation 20:4-6.

" And I saw thrones, and they sat upon them, and judgment was given unto them: and I saw the souls of them that were beheaded for the witness of Jesus, and for the word of God, and which had not worshipped the beast, neither his image, neither had received his mark upon their foreheads, or in their hands; [these are the Tribulation Saints] and they [ the Throne Sitters' and Tribulation Saints']lived and reigned with Christ a thousand years.
But the rest of the dead [the wicked dead] lived not again until the thousand years were finished. This [the Throne Sitters' and Tribulation Saints'] is the First Resurrection.
Blessed and holy is he that hath part in the First Resurrection: on such the Second Death hath no power, but they shall be priests of God and of Christ, and shall reign with him a Thousand Years."

Satan is not casted into the 'Lake of Fire' at this time along with the Beast and the False Prophet because he will be loosed for a short time after 1000 years.

The binding of satan shows that God can stop his evil work when He is ready and without sending the armies of Heaven to do it.

          At that time, God will empower a single angel to seize, handcuff and imprison him.

The character of the chain isn't the most interesting, it's the fact that satan can and will be bound and confined in a place where he can't get out for 1000 years.

         While nothing is said about his angels and demons or other evil powers of the air; they too will be powerless during that period.

Objections have been raised about the possibility of a spirit being bound with an iron chain.

        In 2 Peter 2:24 and Jude 6, the angels who sinned and kept not their First Estate and who are now reserved in chains, in darkness unto the Judgment of the Great Day [the Great White Throne Judgment].

The Angel, who has the 'Key' of the Bottomless Pit, is the same angel that Paul saw when the "Fifth Trumpet" sounded in Revelation 9:1-2, who seems to be the keeper of the key of the bottomless pit.

While satan is the...
'Prince of the powers of the air', Ephesians 2:2; 
and the 'God of this age', 2 Corinthians 4:4;
and the 'Ruler of the powers of darkness, Ephesians 6:11-12;
and whose position is so exalted that even Michael the Archangel dare not insult him, Jude 9; and while he has great power and influence, he is not omnipotent because One Angel, not called a strong angel, is able to take and bind him.

The Interval Between 
The Fourth and Fifth Dooms.
Satan Bound for a Thousand Years.
Revelation 20:1-3.

"And I saw an angel come down from heaven, having the key of the bottomless pit and a great chain in his hand.

And he laid hold on the dragon, that old serpent, which is the Devil, and Satan, and bound him a thousand years,

And cast him into the bottomless pit, and shut him up, and set a seal upon him, that he should deceive the nations no more, till the thousand years should be fulfilled: and after that he must be loosed a little season."

        Satan is called four different names 'Dragon', 'Serpent', 'Devil' and 'Satan'. From these and the fact that he can be bound shows that he is a person because an influence or a principle of evil cannot be bound.

The destruction of the great army will be supernatural and as there is to be great hail to fall from heaven on the enemies of God when the Seventh Vial is poured out, which is included at this time, may be the means God will use, because it was the way that the enemies of Israel were destroyed on the same battlefield in the Battle of BethHoron in the days of Joshua, Joshua 10:1-11

The words in Revelation 19:21, "and all the fowls were filled with their flesh," will fulfill the words of Jesus: "For wheresoever the carcass is, there will the eagles [birds of prey] be gathered together." Matthew 24:27-28.

The Feast in Revelation 19:17-18 is described in the Old Testament, in Ezekiel 39:1-22.

         Also in Ezekiel this same chapter, it tells of the House of Israel, the occupants of Palestine in that day, shall be seven months burying the bones of the dead, the flesh having been eaten by the birds and beasts of prey and the wood from the weapons , army wagons, spears, etc, shall last the inhabitants of the land for fuel seven years, so that they will not have to take wood out of the field, nor cut down any out of the forests.

"And I [John] saw an angel standing in the sun; and he cried with a loud voice, saying to all the fowls that fly in the midst of heaven, [buzzards, vultures, eagles], Come and gather yourselves together unto the supper of the great God;

        That ye may eat the flesh of kings, and the flesh of captains, and the flesh of mighty men, and the flesh of horses, and of them that sit on them [ordinary soldiers], and the flesh of all men, both free and bond, both small and great."

Fourth Doom
Antichristians Nations
Revelation 19:21

"And the remnant were slain with the sword of him that sat upon the horse, which sword proceeded out of his mouth: and all the fowls were filled with their flesh."

The destruction of human life will be so great in the Battle of Armageddon, that God will prepare for it in advance.

After the Battle of Armageddon is over, satan will be bound and cast into the 'Bottomless Pit', where he will be 'sealed up' for 1000 years.

         This is the last act of the Tribulation Period.

Third Doom.
The Beast and False Prophet.
Revelation 19:20

"And the beast was taken, and with him the false prophet that wrought miracles before him, with which he deceived them that had received the mark of the beast, and them that worshipped his image. These both were cast alive into a lake of fire burning with brimstone."

Before the destruction of the army of the Antichrist, he and the false prophet will be cast 'alive' into the 'Lake of Fire.'  This shows that they are not systems but persons. They will be cast in without dying and will be still there and alive when satan is cast in 1000 years later.

Zechariah says "Behold, the day of the Lord cometh," The Day of the Lord is the Millennial Day, For I will gather all nations against Jerusalem to battle; and the city shall be taken, and the houses rifled, and the women ravished; and half of the city shall go forth into captivity, and the residue of the people shall not be cut off from the city.
Then shall the Lord go forth, and fight against those nations, as when he fought in the day of battle.