The Coming of the 200 Million Horsemen
From Apocalypse - Letter by Letter: A Literary Analysis of The Book of Revelation
In 9:13-16, John begins informing the reader that the objective of the second major phase is indeed the whole world. Then, there can be only one reason why the faithful of the religious orders tell unanimously and universally the "sixth angel" to loose the "four angels" bound at the Euphrates: not that the Church is making very slow progress; not that the Church is temporarily making no progress at all, either merely in a particular region or in the entire world; but that the Church is losing ground everywhere, that evil has grown so great as to have become alarmingly advanced, even in the Church, in its highest ranks.
The faithful of the religious orders will not meet and vote on the matter, obviously; rather, they will desire in their hearts and think in their minds, that God should begin the painful process of removing the many evils on earth and in "heaven," the Church. Even the faithful among the laity will sincerely pray: "...thy kingdom come, thy will be done, on earth as it is in heaven." When the salt is no longer preserving, when corruption is consuming so many, then, it will be time.
God knows all, and He has marked the exact hour and day and month and year for the "four angels" bound at the Euphrates to be loosed upon mankind. No one is more exact than God is. No one. Watch the religious orders: they will be the signal. Already their ranks are thin.
So amazed at the number of "cavalry" was John, that he did not put the connective "kai" after it, but only a comma. To make it clear to the reader that the number is to be understood as literal [but approximate, of course], John added: "I heard the number of them."
In John's day, the population of the entire Roman Empire was about 125 million; and one out of every ten could be trained and maintained in the military. The 200 Million Horsemen, therefore, according to the ancient ratio, which has changed little in modern times, suggest a population of TWO BILLION.
John, by human sagacity alone, would have known that the vision was about an event very far in the future. Those who confine the Apocalypse to the Roman Empire are quite in egregious error.