9:16 And the number of the armies of the horsemen was two hundred million; I heard the number of them.

And the number of the armies of the horsemen was two hundred million;

Most scholars believe this isn't a literal human army. Logistically, to field this size army would cause much societal and political upheaval. Maximun mobilization in World War II was about 70 million men. On the other hand, if the petroleum fields are cut off or destroyed, much of the rest of the world will come looking for the oil. This also explains the use of horses.

By looking at the rest of this chapter, the descriptions indicate these forces are demonic "armies". And amazingly, the translation rendered here is "the number of the armies" was 200,000,000. Actual demon count may be higher! Remember, we fight against the WORLD FORCES OF THE DARKNESS (demons and their 4 leaders from the Euphrates River), against the spiritual forces of wickedness in heavenly places (Ephesians 6:12-13).

I heard the number of them.

What John sees in this SIXTH TRUMPET is so incredible that the voice of the altar reinforces the number by verbally SAYING it to him. John goes on in the rest of the chapter to try to describe through spiritual eyes these demonic forces, and how they will operate.