The army of locusts was allowed to torment those without the seal of God on their foreheads, but not kill them, for five months (vs. 4-5).
This is the first place in the book of Revelation where a specific duration of time is given, but it will not be the last. Now historicists agree that one day, in prophecy, equals one year, in history. This principle can be found in Daniel 9:24-26, the seventy week prophecy. There are 69 weeks from the going forth of the commandment to restore and build Jerusalem to the coming of the Messiah. There are seven days in a week, so 7 x 69 = 483. The decree to restore and build Jerusalem was given to Ezra in 456 bc. If one day equals one year, then 456 + 483 = 27 ad, or the exact year in which Jesus was baptized and began His public ministry, in which the title of “anointed one” applied officially to Him. If you are interested in the seventy weeks prophecy in Daniel, there is an excellent exposition of it here.
Following the principle established by Daniel, five months means 5 x 30 or 150 years. So let us assume that this torment, but not killing, of those without the seal of God lasts 150 years.
Now if we accept that the Mohammedan armies were the army of locusts, then we must begin counting time from 612, approximately. This is the year when Mohammed began publicly preaching Islam, after receiving the vision from the fallen angel. Ten years following the giving of the vision and the beginning of public preaching was the Flight of the Prophet in 622; this date is well-established. (Here is a brief biography of Mohammed.) By the time of Mohammed’s death in 632, Arabia had become the first province under the rule of Islam: one former Roman province fallen.
In 638, Jerusalem, Palestine, and Syria came under the rule of Islam. Two more former Roman provinces fallen.
Egypt fell to Islam in 642, Persia in 651, and North Africa in 698. Three more former Roman provinces fallen.
In 711, Spain fell to Islam. Seven Roman provinces fallen. In 732, the Mohammedans tried to take Gaul, but were defeated by Charles the Hammer in a great battle at Tours and Poitiers. The Mohammedans retreated back to Spain, but battles and conquests in many parts of the former Roman Empire continued.
In 762, Baghdad was founded as a capital of the Abbasid dynasty of caliphates. The caliph was the successor of Mohammed. The dynasty which had been displaced by 762 were the Umayyads, and were the dynasty under which all the conquering had been ocurring, beginning with Arabia (Timeline of the Islamic Empire.) The Abbasid dynasty was known for its pursuit of science, arts, and literature, not conquest.
Thus 150 years from the beginning of Islam, to the end of the conquest of the second third of the Roman Empire.
To be continued …
Update: continued in Revelation 9: the fifth trumpet of torment, but not death