The Him referred to on the horse, is Christ. Revelation 19:11.
They will have partial success or so they think, a half of Jerusalem will be captured and enslaved (Zechariah 14:2-3). The battle line will extend from Esdraelan down to Bozrah, about 180 miles. There will be no atomic bombs or total destruction of mankind as is sometimes said it will ultimately be a devastating defeat for the forces of evil and all those in alliance with the Devil. There will be a fierce battle for Jerusalem and plenty will die. We are sure of this ultimate defeat from a number of scriptures. Revelation 17:14, also Revelation 19:20,21 and Chapter 14:17-20.
14. These shall make war with the Lamb, and the Lamb shall overcome them: for He is Lord of lords and King of kings, and they that are with Him are called, and chosen, and faithful.
The mountain district of Megiddo which overlooks the great plains of Esdraelon is a historic place in the Bible it is not an area that is insignificant. Here Barok defeated the Canannites (Jude 5:19), Gideon defeated the Midianites and the Egyptians, Josiah (2 Kings 23:29).
But why would the armies of the world gather together against God, why would they be decieved by the Devil to fight his war. The answer lies in the 7 years of tribulation following the Rapture. Revelation 8:7 to 11:19 follows what happens when 7 trumpets are blown by 7 angels over a period of time. Each trumpet is followed by a judgement on the earth and mankind. Following these trumpets sounding the earth and mankind will go through further torment brought about in Revelation 15:1 to 16:21. Here we have angels pouring out 7 vials upon the earth. All these together make man even more hateful against God. In Revelation 9:20,21 we read of mans (humanities) disregard for God.
20. And the rest of the men which were not killed by these plagues yet repented not of the works of their hands, that they should not worship devils, and idols of gold, and silver, and brass, and stone, and of wood: which neither can see, nor hear, nor walk:
21. Neither repented they of their murders, nor of their sorceries, nor of their fornication, nor of their thefts.
Also in Revelation 16:9 and 11
9. And men were scorched with great heat, and blasphemed the name of God, which hath power over the plagues, and they repented not to give Him the glory.
11. And blasphemed the God of heaven because of their pains and their sores, and repented not of their deeds.
Although you get a picture that God is picking on humanity, there is a way that all the suffering can be stopped, and that is by mankind acknowledging God. Unfortunately such is the hate and depravity of man, that they can only see their own circumstances and selfish needs. All punishment even now is dependent on the criminal doing the deed. If they didn't commit the crime there would be no punishment.
It is this period then that draws all mankind together to listen to the Devil and make war against the coming Christ. That is all those that have the mark of the beast or who are against God.
There will be those who like the devout Jew will not bow down to the Devil and they too will be targets of this army. A more indepth description of this time at the end is in Zechariah 12 to 14. Here we have the story of the restoration Judah, and the refining of the faithful (Revelation 13:9). It is in Chapter 14:2,3 that we are told Jerusalem will suffer but only for a short time.
2. For I will gather all nations against Jerusalem to battle, and the city will be taken, and the houses rifled, and the women ravished, and half the city hall go forth into captivity, and the residue of the people shall not be cut off from the city.
3. Then shall the Lord go forth, and fight against those nations, as when he fought in the day of battle.
The Lord Jesus Christ will then put an end to the war and to this period of time He will stand on the Mount of Olives and make a way of escape for the Jew before Judging the nations and bringing in the millennial reign of Christ.
All the soldiers that participated in the war will be killed. So much will the carnage be that in Revelation 14:20 where the carnage is likened to a wine press, it is said that the blood which came out of the wine press was deep enough to reach 'the horse's bridle' and its length was 'a thousand and six hundred furlongs'. Following on from this in Revelation 19:17,18 the fowls of the air are invited to eat of the flesh of the soldiers and kings gathered for the battle.
17. Come and gather yourselves together unto the supper of the great God.
18. 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, and the flesh of all men, both free and bond, both small and great.
And just in case you thought some might escape from the battle we are given another reminder in verse 21 of the same chapter.
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 sword talked of here is not a literal sword but depicts the 'Word of God'. Throughout the Bible the Word is described as a 'two edged sword' or a sword which cuts to the marrow.
This is the battle of Armageddon, a major confrontation between good and evil, between the people siding with the Devil and those of God. It is quite clear who wins and following on with the study of 'the judgement of the living nations' you can find out the destination of those that sided with the Devil. Armageddon is the gathering the start of the end and is an apt name for the 'final' battle as it is come to be known. But it is not the end of the Devil and is by no means the final battle.