We already know that we are looking for an assault against the Byzantine Empire which begins sometime after 762, the date that marks the end of the fifth trumpet. The Turks are the only power to assault the Byzantine Empire following 762 (The Sixth Trumpet: 1056-1453, pg. 78).
That the assault of the sixth trumpet against the Byzantines cannot be attributed to the Mohammedans of the fifth trumpet:
Constantinople sustained two great sieges … the first siege was in 673-77, under the caliph Moawiya; his fleet blockaded the capital for five years; but all its efforts were frustrated by the able precautions of Constantine IV.; ‘Greek fire’ … played an important part in the defence; and the armada was annihilated on the voyage back to Syria by storms and the Roman fleet. The second crisis was at the accession of Leo III., when the city was besieged by land and sea by Suleiman for a year (717-18), and Leo’s brilliant defence, again aided by Greek fire, saved Europe. This crisis marks the highest point of Mohammedan aggression, which never again caused the Empire to tremble for its existence.”
“Roman Empire, Later,” The Encyclopaedia Britannica, Vol. 23, p. 514.