You can see that this passage deals with four evil angels, who were prepared to kill a third of mankind. The previous Fifth Trumpet described demonic locusts ascending from the Abyss. Their leader is named Abaddon or Appolyon. (Revelation 9:11) Both names mean “destroyer.”
The demonic locusts are said to have the appearance of horses prepared for battle. (Revelation 9:7) According to the Food and Agriculture Organization of the United Nations in 2006 there were only 58 million horses on the face of the earth. It seems that the 200 million horses of the Sixth Trumpet may actually be the demonic locusts of the Fifth Trumpet. Of additional interest is the Greek word translated as horsemen, hippikos (Strong’s G2461). This word is more closely related to “equestrian” and “horses” than to men.
Also, it would seem that the 200 million horses of the Sixth Seal have nothing to do with the Sixth Vial, or Bowl.
For many years it has been assumed that this prophecy relates to China. After all, China is large enough to have a 200 million man army, but we have seen that that number appears to be unrelated to this passage.
I personally believe that the Kings of the East are the nations listed in Ezekiel 38:3-6 (Meshech, Tubal, Persia, Ethiopia, Libya, Gomer, and Togarmah). The sixth angel dried up the Euphrates River (traditionally the division between east and west). If you look at a map, with the exception of Ethiopia and Libya, all the listed nations must cross the Euphrates in order to reach Israel.
In addition, Bible scholars believe that the Kings of the East that sought to worship the baby Jesus were Parthians. Parthia occupied the countries known today as Iran and Afghanistan. These Magi had to cross the Euphrates to reach Bethlehem.
Please note that immediately following the action of the sixth angel, demonic spirits gathered the kings of the world to Armageddon. (Revelation 16:13-16) Armageddon is not named in the Old Testament. Jewish rabbis believe the so-called Battle of Gog and Magog is the final battle of the Day of the Lord (Ezekiel 39:22) It appears that Gog and Magog and Armageddon are the same event, and the Kings of the East are enumerated in Ezekiel 38:3-6.
The Revelation is such a complex, multi-layered book. When we get to Heaven, the Lord will explain it to us. May His name be praised forever!